Corporate event pricing

I was recently asked to do a prom style shoot at a holiday party at a decent size company.
So far we have exchanged emails with the person responsible for the event organization and the budget and here's what I know so far:
1. It's going to be around 400-500 employees with spouses, so roughly around 900-1000 people. Some people might want to get their picture taken, some not, so let's say it's going to be half of that amount that want their photos taken;
2. The photo services will be available for about 3 hours;
3. No more than 2-3 shots per person/couple/group;
4. No post processing needed, I will just burn images to a disk and give it to the organizer of the event. He will distribute images via email to the employees;
5. No prints are necessary;
6. The setup should be festive, but not too holiday'ish.
7. I will have enough room to setup up lights and have enough area for the equipment.
8. I do not know the budget for the photos.

I've done some calculations and I've figured, that it almost impossible to cover even 250 couples (3 hours = 180 minutes, considering 1 minute per couple/person).
Another consideration - I'm not really sure how much to charge, considering that even if there is no post processing needed, I would still need to spend some time in front of the computer to at least throw out the bad ones. Hopefully, I won't need to do any major adjustments.
I don't have a "festive" background, which I would need to purchase as well, but again, this is rather my problem. Maybe I'll look into renting one.

So, it all boils down to the same basic question - how much do I charge? I have done a similar style of shooting before, helping a friend shooting a wedding, but this is a bit different.

Thank you very much in advance.

It's highly unlikely that anything you shoot would ever be valuable to you in the future. You're not likely to use any of it for print sales down the road, or need it for licensing use later, right? Who's going to buy photos of someone else's party? Unless there are celebrities there, probably not.

Usually those kind of events aren't even "come pose for a photo" or "would you like your picture taken with your boss" kind of thing. It's more about capturing the candid shots and maybe the food spread, etc.

If it were me, I'd charge them a fair hourly rate for my time, burn the photos to CDs and collect my check. No post, no hassle, no problem.

Just my opinion.

Actually, there won't be any candid shots, food spreads or anything like this.
It will be a setup in the corner, people will come in, snap-snap, next.
However, you're right, those shots won't have any value to me and I'm not going to use it for print sales or for licensing use.
No celebrities either.

I guess, I'm trying to determine an acceptable hourly rate and try not to shoot myself in the foot, undervalue photography as a business and not to scare the client.
I've seen some suggestions around $100-$125/hour or since it's going to take about 4 hours (half-day), just charge around $400 total.
What do you think?

In my neck of the woods event photography goes for around $125-$250 an hour depending on usage and amount of time that the event will be covered. That is in Nashville, TN so I would assume that the going rate is higher in LA.