I'm afraid I feel a bit differently to the other posters.
Personally I'd be a bit miffed if I had to pay for my meal, after I'd already forked out for travel expenses, outfits, hotel, gift etc. You have specifically invited your guests to celebrate your day with you...what are you going to do if they turn around and say we'll come to the ceremony, but we can't afford the meal.
If your budget was really that small, I'd be looking at alternatives like a cold fork buffet, or bbq. And I would only have one set of guests that stayed all day so I wouldn't have to be feeding the evening guests too.
…always got her eye on biscuits 