What's the menu (food cost)?
What is your kitchen help cost?
What is your server help cost?
Are you providing Linens, tableware, etc.
Personally, I'd add up ALL my costs, then add on what you want to earn, and then quote the total. I do NOT quote per person prices for small parties because my costs, and fee, does NOT go down proportionally if the number of persons decreases.
EXAMPLE: You quote, say, $50/person, thinking 24 people, comes the event and you've purchased food for 24 and rentals for 24 and labor for 24 and now only 20 people show up. Your gross just went down from $1,200 to $1,000, a drop of $200 and your costs did NOT go down, so your "net" dropped by $200! That's probably 25% to 50% of your profit!