You have got to be kidding!
I have to ask, do you really know how much work it is to cater and feed 300 people??? A good friend shouldn't expect you to do that much work for so little pay, after you cover food cost, business expenses & labor whats left???
I'll probably get chastised for this but this is just another case of you really shouldnt be doing this if this isnt what you do for a living, someone else or even yourself if your a caterer could make a nice buck from a job like this.
Some people see kindness as a weakness and take full advantage of it, I think your probably a real nice guy and your buddy is taking advantage of you! You should be 3 times that price minimum! Bare minimum!