JCWhitney.com has vinyl for $150 and carpet for about $120. You might find original vinyl and carpet on ebay or car-parts.com.
If you like try to do things yourself, w/a little cutting sewing, glue, and a heat gun, you can get pretty good results. I haven't tried to do one out of vinyl yet, but here are some pics of ones I have done with carpet.
I glued the carpeting to the vinyl, so it could be removed as one piece, it also helped to keep the carpet smooth.
If you aren't after an em look, just covering the floors, a few members here have been happy(once the fumes are gone) with a DIY roll-on truck bed liner. You might also look into the Lizard Skin coating, it is also DIY and provides both sound deadening and thermal insulation.
