see if you can't find a used camera store in your area, you should be able to pick up filters for fairly cheap. They can always be held in place with some camera tape or gaff tape if they don't quite fit right.
Tobbacco filters would offer a hint of the sepia-tone feel without totally ruining the color. Also, you can white balance (assuming you're using video) to colors other than white for interesting effect. The best thing to do is take the camera to the store and test some filters out to get the effect you're looking for.