While I personally haven't catered towards any events, I know plenty of people that do, including a neighbor who runs a food truck and catering business. I help out whenever I can with both.
Most of the time he quotes per person. I would say that $30 a head is common. It depends what you want your margins to be. You should be aiming to have your complete overhead costs @ 30-35% of what you charge. However, you can always adjust that margin based on other factors-maybe it's a charity event, maybe it's a buddy, maybe this event has the potential for future events and you can take a hit in the pocketbook now if it means you get another gig with the same client.
Some people do take their food cost x 3 to get their number, however, that leaves you with bad margins in my opinion.
Total your cost of
food (figure in meat shrinkage and sides) +labor+ gas to get there+ wood/charcoal + utensils + any other incurred expenses (insurance, taxes, whatever)
and divide that total number by the amount of people you plan to serve
multiply that number x3
The number you end up with is your cost per person minimum. You should strive for more, but it depends on your overall business goals (if you want to run it as a business)
Food cost = $150. Labor cost=$60. Gas=$30. Wood=$40. Utensils = $20. Insurance = $5.
Total cost is $305
You plan to serve 50 people.
$305/50= $6.10 (cost to serve each person)
$6.10 x 3 = $18.30....this is the MINIMUM you should be charging if you want a decent margin, and to be paid for your time. Caterers, do very good on margins.
Quoting by the hour just leaves so many undecided factors on the table, I just wouldn't do it if that's me.