It could be done at home, if you've got patience and a sewing machine. You basically take the original apart, and use it as a cutting pattern, then sew the whole thing back together. Our seats are pretty complex, with like 15 different pieces, so it may be a bigger project than you'd want to tackle. It's not hard per se, but it takes some attention to detail. I know an old guy who totally recovered his Model A interior by hand, with a treadle sewing machine (works with a pedal) and he did a really passable job. They guy was like 70 when he started it, and had never sewed in his life!
One step removed would be the ATD1 kits in the vendor's section. It's just under $600 IIRC, but people seem to like them and have good luck installing the kit at home. You can get matching panels for doing the doors and such at the same time. I've thought about doing it from time to time, but ended up buying an AccessPORT instead. go fast > look good.
Finally, I'd have to guess that having a pro do it would be close to $1000, probably more if you get some really nice material like an ultrasuede or microfibre, but it would likely be show-quality.