And I have looked at Peru's Parks as well and no hint of any differential - it seems that they are only loading MP!
https://peru21.pe/lima/establecen-nuevas-tarifas-ingreso-areas-naturales-protegidas-p eru-138899

Slightly off-topic, bit I checked Greece (Acropolis) and they provide free entrance to for example this very specific subgroup:
Parents of multi-child families and their children up to the age of 23, up to the age of 25 if they are doing their military service or studying and regardless of age if they have disabilities, upon presentation of a certified multi-child pass from the Supreme Confederation of multi-child parents of Greece (ASPE).

Well they deserve it more than those feather bedded freeloaders from ICOMOS -
http://www.archive.usicomos.org/Membership/ICOMOS_Card_Benefits.htm

This probably constitutes an illicit discrimination against multi-child parents from other EU countries. EU countries must not discriminate any EU national.

Els, I have put together the pricing differentials at Thailand's WHS for the Connection
Ayutthaya
Individual Temples have individual prices e.g Wat Phra Si Sanphet 10B for Thais or 50B for foreigners. In addition there is a "6 Temple ticket" for foreigners at 220B
Ban Chiang
30B Thai/150B Foreigners
Dong Phayayen-Khao Yai
Locals 40B/Foreigners 400B
Sukhothai
Tickets are issued for each of 3 "zones" (Cent/North and East. It used to be 5 and Web reviews often still say it is but tickets had, as of Dec 2017, been discontinued for the Southern and Eastern zones) @100B per zone for foreigners - 20 (I think) for Thais
Thungyai-HKK
Locals 20B/Foreigners 200B

It appears that Thai dual pricing is somewhat "notorious" as it applies to commercial "attractions" as well i.e It is ingrained into Thai culture!
See - http://www.2pricethailand.com/how-they-trick-foreign-tourists-into-paying-more/

I have remembered that New Zealand rather surprisingly also charges Foreigners more at Waitangi ( A Tentative List site) - presumably on the "Cost of Provision" argument -though I did comment on this in my review of some years ago that you might have thought they would be proud to show their National Monument to foreigners at at least the same price as they pay ($20 v the $40 they charge foreigners) ! See -
http://www.waitangi.org.nz/experiences/waitangi-treaty-grounds-day-pass

Thanks for Thailand. Esteban Cervantes has also sent me Costa Rica!

Here I send the information on the differential prices in my country, that could be of use to you in a future. Costa Rica is defined as a mid-income country, but we're also a very expensive country, as we sustain an extensive welfare state. I found the prices for residents a bit ridiculous, though, like the third part of an average lunch...and of course, the prices for non-residents are too high.

I only include prices for adults (children have in all cases preferential rates, as well as seniors with an special ID, students with a high school/college ID also in most parks)

Talamanca Range-La Amistad Reserves:
La Amistad National Park: Residents: ₡800; Non-residents: $10 (₡5.638 at today's exchange rate).
Chirripó National Park: Residents: ₡4.000 (not including transportation San Gerardo-Crestones base), Non-residents: $18 (₡10.148 at today's exchange rate, not including transportation San Gerardo-Crestones base).
Tapantí-Macizo de la Muerte National Park: Residents: ₡800; Non-residents: $10 (₡5.630 at today's exchange rate).
Barbilla National Park: Residents: ₡1.000; Non-residents: $5 (₡2.819 at today's exchange rate).
Hitoy Cerere Biological Reserve: Residents: ₡1.000; Non-residents: $10 (₡5.630 at today's exchange rate).
Las Tablas Protected Zone: could not find related information.

Cocos Island National Park (exception):
All visitors: $50 (not including astronomical cost of transportation Puntarenas-Cocos island)

Guanacaste Conservation Area:
Santa Rosa National Park: Residents: ₡1.100 (not including $2 camping costs per night); Non-residents: $15 (not including $2 camping costs per night, ₡8.457 at today's exchange rate).
Guanacaste National Park: Residents: ₡1.100; Non-residents: $15 ( ₡8.457 at today's exchange rate).
Rincón de la Vieja National Park: Residents: ₡1.000; Non-residents: $15 ( ₡8.457 at today's exchange rate).
Bahía Junquillal Wildlife Refuge: Residents: ₡2.000 (not including camping costs); Non-residents: $19 ( not including camping costs, ₡10.712 at today's exchange rate).
Horizontes experimental station: Residents: ₡1.000 (not including lodging); Non-residents: $10 (not including lodging costs, ₡8.457 at today's exchange rate).

Stone Spheres of the Diquís:
Finca 6 archaeological site: Residents: ₡1.000; Non-residents: $6 (₡3.383 at today's exchange rate).
Batambal, Grijalva, El Silencio sites: could not find related information.

It seems that the practice of charging Foreigners more extends in Central America beyond Honduras and Costa Rica!

El Salvador
Joya de Ceren - $1 "Salvadorians and Central Americans" $3 - foreigners
see - http://8319-presscdn-0-95.pagely.netdna-cdn.com/wp-content/uploads/2014/09/DSCN9695.j pg
This link goes back to 2015 but I can't find anything definitely more up to date. Can vantcj1 provide anything different?

Guatemala
Qurigua - Q20 for locals, Q80 for foreigners
Tikal - almost certainly this too has a price differential but it is proving VERY difficult to discover what the local price might be as Web sites concentrate on the arrangements for foreigners. These seem designed to ensure that, as far as possible they are paid at international entry points or directly to a bank in order stop corruption!!! - See http://www.tikalpark.com/#!/parkreg
Antigua Guatemala - e.g "the Ruinas de Santa Clara, Ruinas de San Jeronimo, Ruinas La Recollecion and the Museo Capuchino charge Q40 for foreigners (locals Q2)

I have made a check and it seems that the price for Joya de Cerén remains the same.

Thanks.
Any chance of you discovering the price for locals at Tikal?? Searches in Spanish would seem to be required

Turistas nacionales: Q 25.00.
Turistas extranjeros: Q 150.00.

https://aprende.guatemala.com/cultura-guatemalteca/actualidad/precios-horarios-parque -nacional-tikal-peten/

A few more - and 3 new countries operating differential fees

Ghana
Cape Coast Castle - Locals 3 Gh Cedi, Foreigners - US$ 7 or equiv in Cedi (c31)

Haiti
Historic Park - Locals 25 Gourdes, Foreigners - US$5 or 200 gourdes

Botswana
Okavango - 120 pula pd. I can only find the cost for foreigners but at nearby Chobe (not a part of the Okavango inscription) the cost is P120 for foreigners (cUS$12) and P10 for citizens so I assume Okavango will be the same.
Tsodilo - I found this "Admission to Tsodilo Hills is free, and visitors must report to the headquarters at the main camp (called Rhino). Camping is also free at the campsites around the area, but they are extremely basic and run by the National Museum."

Not anymore, according to 2017 Tripadvisor reviews. Will try to find the pricing

Seychelles
Vallee de Mai
" All non-seychellois visitors are required to pay an entrance fee of 20 Euros."

The other way around:
"Xidi Village: CNY 104; Hongcun Village: CNY104
From November 1, 2017 to February 28, 2018, both villages will grant half-price tickets to all foreigners and Hong Kong, Taiwan, and Macau residents."