Hey KyleRayner,
Almost all of the Mousefest events last year were free to attend. I think there were a couple of events that cost money (like a Fireworks Cruise). Some meets are at restaurants and some were at nightclubs, which might require some extra cash. You can choose whatever meets or events you want to attend, depending on whether you think it might cost a little extra or not. The Mousefest website will have detailed descriptions of the events, so you should be able to ascertain whether it will cost anything to participate.
I just attended the land portion of Mousefest 2006 and I will again this year. The time during Mousefest is Value Season for resort rates, so that will save you money. If you have an annual pass, rates could be even lower, if they offer a discount during that time, which I believe they did last year.
Meals, tickets, etc., will be the same as any other time during the year. I don't know if they'll have any specials going on; just keep an eye on the boards or visit AllEarsNet.com.
Hope this helps. Post any additional questions you may have. You'll get lots of help from us DISers!