What to charge is the least of your worries. Although it is a little late for this now, the best preparation for shooting weddings is to shoot several weddings as a second shooter for an experienced wedding photographer. Although you probably won't do everything the same way as your mentor does, you will get some very good exposure to what to expect when shooting weddings, how each wedding can be different, and learn how experienced wedding photographers deal with the various "people" issues that shooting weddings presents.
If you're determined to go ahead and shoot a wedding as the primary photographer without any previous experience as a second shooter or assistant, then you should probably consider the following with regard to pricing and expectations:
- Emphasize your lack of experience with actually shooting weddings to the customer well in advance. It's always better to beat low expectations instilled before the fact than it is to try and explain not hitting high expectations after the fact.
- If you regularly shoot paid commercial jobs, discount your regular rate by a significant amount (25-50%). If you don't regularly do paid work for strangers, then either don't charge anything or, at the maximum, charge for your direct expenses to attend and shoot the wedding: transportation, meals, lodging (if applicable), any gear you might rent only for the wedding, etc. Again, this helps lower the expectations somewhat in advance. Emphasize that you are only pricing this way because it is your first wedding, and that their friends, relatives, and acquaintances should not expect similar pricing in the future should they like your work from this wedding.
- Include language in the contract (yes, you need a contract even if you aren't charging anything) that limits your liability if the clients are not happy with the results. Never, ever shoot a wedding without a contract!
Also consider the following questions related to "Help! I'm shooting a wedding in two days/weeks/months with zero experience as a second shooter or shooting other similar types of events in similar settings."
What is the highest acceptable ISO to use for weddings with Canon 7D?
How do I prepare best for my first wedding photography event?
How do I prepare best for my first wedding photography event? (Duplicate question with different answers)
Portrait photographer asked to shoot a wedding — how should I respond?
Tips for photographing a wedding
What are some tips for shooting in low light?
Is there a trick to shooting large group portraits without blinkers?
How to pose and arrange people in a group shot?
