As everyone has already said, this is a business, so it doesn't matter if it's 50 people or 500 people, you cost everything out and then price it accordingly so that you make money and is worth your time.
And as landarc mentioned, a wedding is a bit different because the bride and groom (usually the bride) has ridiculous expectations on their most important day of their lives. So don't skimp, don't cut corners, and price it like a big ticket venue. Provide more food than you usually would, do something special with the meat, or spend more time preparing than you would any other catering event, and price accordingly. Last thing you want to do is come up short.
Or, do as I do, both in my BBQ and my photography business. I simply don't do weddings. People beg, the money can be good, but I just don't do weddings. That may be a bit extreme, but personally I'd rather do anything but a wedding since expectations are so high, it's such a stressful time for the guests of honor and things can and do go wrong, etc.