The cheapest ones to use that are fully automatic are the Vivitar BV** DB (databack) or Vivitar EZ motor date, they do it all, but flash distance and some pic quality will be an issue. If you have a tight trail ( 3 to 5 yards) they will be fine.
Oh, forgot, I believe they are mechanical shutters, so you will need a soleniod set-up.
Toothwrecker, even if the shipping were/camera, thats not a bad price. When Walmart lowered the price to $22 + tax about a year ago, I bought all they had here. If you can get a better deal, thats great, but about $20 with shipping isn't a bad price at all.