Freelance Pricing

I'm a newbie to the Freelance business, although my previous work was paid for in a barter style, in that the people I shot for, provided the passes(backstage) and accommodations. The new request is during the next event and they want publicity type photo's (one of there chef, crowd shots, etc) and approx 1 - 2 hr of time. Could some give me a way to estimate for this service, client needs the info, prior to event.