Chainat Bird Park charges Thai adults 30 baht, foreigners 100. Definitely not the biggest price increase out there, but still the principle remains.
Thankfully we got in for 30; I assume as we arrived with less than an hour until they closed, and spoke Thai.
Good for 30 baht. 100 baht is reasonable (if all paid this it would be fine). One thing that I noticed is that all signs were in Thai only. Seems very unfair to charge non-Thais 3 times more, then not even bother to provide information in English.