There are a few arcade type games that they charge for because you earn tickets for prizes for it, but other than that, all of the great attractions are free, as are a ton of arcade games.
There is plenty of opportunity to spend money, though. For example, you can buy a tape of your ride on Cyber Space Mountain, or you can by the pieces to make the toy you created at Sid's Create A Toy (or something like that). I guess it really depends on whether or not you are the type of person who likes to buy the extras when you are doing that type of stuff. I personally have never purchased anything there, and usually only spend money on food and drinks once I'm in there.
Karen