Els, I have put together the pricing differentials at Thailand's WHS for the Connection
AyutthayaIndividual 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 Chiang30B Thai/150B Foreigners
Dong Phayayen-Khao YaiLocals 40B/Foreigners 400B
SukhothaiTickets 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-HKKLocals 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