if you are going to Ayutthaya and planning to go the "fake" floating market, remember when u near the gate where u need to pay ticket to enter just keep quiet and dont talk among yourself.

They will thought you are Thai and can avoid paying 200 baht. Only non Thai national need to pay(written in Thai). When questioned a reply in Thai usually solve the problem

A good friend who visit recently was stopped at the gates and ask to pay 200 baht for entry ticket. They give themself away by talking too loud

200 baht get u a free boat ride around the rather small and disappointing man made like "canal"

If you do  understand Thai fluently there is a free open air theater show about a war during the kingdom of Ayutthaya.

Some of the ruin you need to pay entry ticket, same thing again Thai national pay much lesser and some are free for them.

Further up north in Ang Thong u can check out the biggest Buddha figure in thailand and dozens of figurine that portray hell if that is your type of thing. Ayutthaya is a place you can actually drive to from Bangkok, not far around 1 and a half hour, and there is a premium outlet along the way. The ruin looks good during the night some of them have beautiful lights.

Khao Yai is just a village small town and you can check out the various farm or "organic farm" there. Unless you are talking about the national park.