Spend as much as you can beg, borrow, and steal, after all we deserve the best vacation pictures you can get.
Seriously though, it depends on where you want to allocate your discretionary funds. If you want to party every weekend then it's less for vacation and vice versa. But weighing cost vs the potential experience, that's purely personal. When you get to the old folks home what are the pictures you took and the pride in saying been there, done that, worth?