$75 is definitely VERY reasonable. I have that same cage, and even wholesale, you can't get it for less than $90 (pet stores charge $160).
And yeah, you can tell by looking at him he's malnourished. It's interesting to me that the owner knew enough about gliders to get him a huge cage, fleece toys, and a stealth wheel, yet didn't know that pellets were bad or realized just how poor he looks as a result of eating that mess.
I hope you get him. He needs someone to take care of him.