In many cases its just as easy to do 60 or 90 as it is to do 30 for a catering. There is money in numbers when it comes to catering, You have to do all the running for the food, prep, setup, serve, knock down and clean up, and then have a few cocktails. The problem with taking all this into account is, the client, in most cases can't see it, why does it cost so much, like your time isn't worth anything and you should do everything for fee. I always figure my time at $100 an hour when everything is said and done. In many cases this is hard to do at $10 to $20 a plate, but then again a small catering is hard to make money on. If I'm catering a lunch, the amount of my time is less, if I have a 5 course dinner, it could be 12 to 15 hours involved at a cost of $75 to $125 a person. There are two many variables for a stock answer, give more details on menu, shopping, prep and so on...............Take care.............ChefBillyB