@dubshotimage: IMO, charge an hourly rate for the time you spend at the event, and make sure that rate is enough to cover the time you'll spend doing processing later. For example, my rate right now is $100/hr including basic processing, not including prints or files. If I were to include the digital files (and all associated rights) then I'd charge more. If the event requires more post work than usual then I'd charge more - for festival shots you're probably not doing extensive post-processing, just the usual culling, cropping, white balance, sharpening. Weddings, glamour-style portraits, etc all fall under "more post work than usual."
If you feel like you're spending way too much time processing, you may need to either streamline your workflow (e.g. use Lightroom instead of Photoshop), or make changes to your choices as to which types of shots get what types of treatment. As a general rule, I don't think that 1/2 hour processing for each hour shooting is excessive - above, you said 2 days shooting and 1 day post, which sounds quite reasonable.
If the event organizer has a large budget for photography, they get a lot of shots. If they don't have a big budget, you just work for a couple of hours, and they only get a handful of shots.
 OR, the event organizer has a small budget for photography, but you still spend 2 days shooting and 1 day postprocessing, and after all is said and done you realize you made $5.25/hr.