I used to occasionally stop into a National Park in Thailand when out on a road trip. I would show my Thai D/L and pay Thai price.
Then a few years ago they said it had changed and wanted 400thb, I would just turn around. Haven't been since.
Im sure some of the parks are beautiful, but even in Canada if I was on a road trip, I wouldn't pay that price to just pop in for a half hour. I dont even mind the duel pricing in principle, but 5 to 10 times is just extortion.
I dont think the powers that be have any idea what puts off tourists. Starts with being ripped off at airport by porter, then by taxi, then by restaurants, then by attractions, etc. You get home and think I'm never going there again...and then you tell all your friends about your experience.