I have a bench seat I'm going to re-cover. I noticed the burlap under the seat is gone and the seat foam has a 3/4" deep groove in it from the springs. Is there a way to salvage the foam with a more firm piece of foam underneath? New ones are pricey. Is there a better product than burlap to cover the springs?

I have done repairs to the foam and it is pretty easy. Get some foam from another seat or fabric store. Cut out the affected area with either single edge "razor blades" or a serrated steak knife. The blades will become very dull very quickly, so you will need a stack of them. Glue in a repair piece with 3M aerosol adhesive and trim the extra foam with the knife as required.

I have seen them doing custom seat work on TV and they use a tool that looks alot like a plain old electric carving knife like you would use in the kitchen when carving the turkey and stuff like that.It has 2 serated knives that cut very fast and easily,straight through meat,maybe thats what they use to shape the foam with.
Just wanted to tell you that, in case it will help you out with your seat.:D
As soon as I find a piece of foam as a practice piece,my electic carving knife will "mysteriously disappear" for a short time.;)