We've done a lot of behind the scenes tours, all were included in packages we were on so the prices are approximate...
Our favorites were in Epcot:
Aqua Seas where you snorkel in the Living Seas, I think $100/person and 2 1/2 hours long.
Dolphins-in-Depth where you interact with the dolphins, I think $150/person and 4 hours long.
With these you get to go backstage in the Living Seas (obviously

), very interesting for us, especially to learn about how they care for all of the animals and esp. the dolphins!
We've also done Hidden Treasures of WS, around $50/person, 3 hours. This was mostly on-stage, although we got a backstage peak at France and Canada. We learned a lot that we didn't know and found it interesting.
Our next favorite was Backstage Safari at AK, $65/person, 4 hours. We love animals, so this one was perfect for us.
Our least favorite was KTTK, still liked it, however our tour size was fairly large, our tour guide fairly new, and we had about 3 people that asked the same questions over and over in different ways after our guide had already explained everything and it got worse as the tour progressed so it seemed to take forever at the end... Not to say we didn't learn anything new because we did; I'd say about 30% I'd read somewhere here or elsewhere and the rest was new. It would be interesting to try this one again to see how it would be...
HTH
