Well, probably not a lot. I can't remember what size my first purchase was..... but ever since, I've been going to gallons, which are a little over $18 at WalMart (bought one yesterday).
I'm sure there's a size smaller than that though. (Maybe a quart?) Get it and try. What's the worst thing that can happen? You'd have to go back to the store and buy another one. But that wouldn't affect your project at all, because it's just fine to bondo this stuff one section at a time.