I think it all depends on where you want to have it (pool, room, food court tables) and how many people. Is everyone staying at the All Stars?
Unfortunately, Disney won't cater an unofficial event like this and if you're thinking of doing outside catering, I'd make sure that Disney allows it first. Also if you're thinking of including decorations or something maybe check it out first, I wouldn't want stuff you spent good money on to go to waste. Maybe you could call management at the All Stars?
Just another thought . . . if you have a small group, you could take a towncar out to dinner at any local spot, or even meet up at another resort for dinner.
Finally, a last thought . . . I am doing a really inexpensive welcome party through Rainforest Cafe. Their prices are amazing and the catering manager who worked with me on my event is so nice and on top of things! I can send you the menu I received if you want.