I would charge the same as my hourly editing rate. Are they providing all the elements or do you have to create graphics, backgrounds etc? What about format conversions / encoding?
I would guess a minimum one day of work. You should be charging at least $50 per hour.
However, additionally, for one off projects I also have a rule of thumb - I won't do it for under $1000. This is from past experience - once you have back and forth approvals / testing etc involved, seriously it is never worth trying to do a job for $500. If they don't have at least $1000 to pay you then you are likely to have all sorts of problems dealing with them.....