Well I base it on the hour plus prints.
And as far as how much... what are you worth for those 5 hours? If you charge $250.00 for 5 hours (50 bucks an hour), what happens if your there for 7 hours? What if you're only there for 2? Do they want a refund? Are you charging some for your wear and tear on the camera? Do you need to rent gear? What happens if the card crashes? Do you need to buy new cards?
What kind of product do they want? Prints or digital negatives? Do they want them for promotional materials? Are you going to keep the copyright or give them up? Do they want to use these for the inside sleeve for a CD or are they going on myspace?
As you can see... it is almost impossible for us to give specific pricing because of those things and things like your skill level, overhead and tons of other reasons. Plus experience plays a roll too. Some photographers are charging hundreds or thousands of dollars a day for their work. Others will only charge 100 bucks and free food and drinks at the party and give the cd away. You will have to figure out your worth.
Me personally... I'm going to charge $750.00 for 5 hours, 200 for each additional hour, give them a proof cd and 10 8x10's (or 8x12's) for that price. All other images are standard pricing. If they want to use these for pr stuff... I'm going to charge them 500.00 for a one year/shared copyright for 10 images. After that year, we'll negotiate for another year if they want.
What do you think you're worth? You have to decide.