After airfare and pre-registering for the con itself, I usually just scrape together whatever I can manage for other stuff. For the last couple years I've been reserving the room, and I don't have my roommates pay until we're actually there, so I usually just pay for the room with my debit card and use whatever they give me in cash as spending money. Last year I think I had $300 to blow in the dealer's room, which is plenty for me. This year times are tough, so I'll probably limit myself to $200.