Buyer beware of buying seats sight unseen. The 'leather' GSR seats are definitely a step up from the cloth ones, but they're actually not real leather and most of them suffer rough spots from either water damage, sun damage, or neglect. I bought 2 sets on eBay before I found a set that was acceptable, and i'm not that picky.
I paid $380 for a set. Then bought some fronts for like $280, then bought a set of fronts for $400 in person, as they were in GREAT shape and I was done searching around online for something that may or may not be completely beat when it got to my house. Apparently prices have gone down, as this was only like a year and a half ago, and I was watching sets of fronts go for $500 and up.
If you buy on eBay, try and be sure you're not buying junkyard seats that have been rained on, or sitting in a car growing mold under the seat covers. Ask for closeups of the fabric, and ask for pictures of the bottom of the seats. You'll be able to see easily if they've seen excessive moisture, as the metal on the underside of these rusts very easily.
-Nick