Amazon has a sale on Grateful Dead albums (MP3 downloads). The albums are priced $2.99 - $5.99. I did a quick check and most look like they are $2.99 - $3.99.
So if you don't have a bunch of bootleg cassettes rattling around on the floor of your car, this is a good way to build up your collection.
Edit: I scrolled through, and there are a handful that are in the $6-$11 range. And the 160 song Golden Road collection is $64. But most are under $5.