Rush Fees?

[jakejynx.livejournal.com]

Hey all, I'm in need of some advice and don't much know of a better place to turn.

For those who offer items in a rush, how do you determine the rush fees that are associated with them?

In my particular situation, someone is wanting some custom fursuit items, but with my commission list and a convention coming up, I'm really strapped for time. And they want the items by Memorial day weekend (so I'd have to finish and mail it off in about a week). They'd have to be bumped in front of seven people currently waiting. :|

I thought of doing $10 per person that they skipped in front of. Is that reasonable?

EDIT: Thanks guys! A percentage seems like a good idea. :)