Is catering going to be a regular thing for you or just a one off?
I would start and look at what some of the others in the area are charging. Use the forms that Jimmy gave you. If you go to the search link that fpnmf gave you. I think it was the 4th or 5th thread Chef Rob gave a good formula to use for the pricing. It was one of the first posts for the thread. Adjust your price to match what is going on in the area. You do not want to be lower than they are if this is not your everyday thing.
I do not do side Catering at home much. I get depressed when I look at how many hours I spent doing things and figure my hourly rate. People want to beat you up for the price and expect you to do it for almost nothing. Things in a regularly used location will end up being cheaper due to natural efficiencies and cost saving due to bulk purchases and usages. At home the cost of things will sneak up on you, stuff like rubs, marinades, sauces, wrap, fuel, containers and the list goes on. Make a very detailed list of what is needed to make each item, then with the spread sheets you can get a better idea of your cost. Then you figure how much is your time worth and price from that.
I know this does not give you a black and white answer. Fell free to PM me if you have any questions you don't want to ask in the thread.