Agree with Jasonjoseph on the undercutting... you may want to undercut other ppe too!
Altho there is no formula, but I think there are a few factors to consider for every proj,
1) manhr effort in shooting the event (more cameramen or longer event = more salary payout)
2) manhr effort in editing (more camera pts = more footage = more time cost. & No. of revisions?)
3) opportunity cost (you may have to give up a potential 5K proj just to shoot this event)
4) value of the proj to the client (if he is gonna sell each DVD for 10K, I'll charge him sky-high. Just like wat the music industry practise for music copyright)
5) How much the project means to you (who knows, you may want to do it for free?)