I don't have nearly so many miles on my bike as a some of you around here but the miles I have put on my bike have been pretty hard. Three years back on a 45 day moto camping trip my seat started tearing bad. I "field fixed" it with some gaffers tape and haven't been concerned enough since to put any effort into it.
Yeah, that's pretty unappealing...
I'd seen a few threads here about recovering a seat so I figured I'd give it a shot. Decent seats on ebay were at least $60 or so with shipping so I wanted to have a go at it myself. I went to Joanne's and picked up two packages of seat upholstery foam and 2 yards of vinyl. All those items were half off and it came to about $18 for those materials. I also got a Black & Decker electric carving knife on Amazon for $13.
First I cut away the old vinyl, pulled the old staples, and removed the old foam. It pulled right off.
Then I used 3M spray adhesive to stick the two squares of upholstery foam to the plastic base. Then a piece of cardboard and some ratchet straps while the glue set.
Then I just started shaving away with the electric carving knife. Took it nice and slow trying to keep things symmetrical.
Here is my first attempt at covering. Throwing the yard of vinyl in the dryer for 20-30 minutes on low makes it a lot more pliable.
I didn't build the foam up enough at the crotch and I could feel the plastic base of the seat when I rode. No good. Tore that off, and used some foam scraps I shaved off to try and build up more padding. I used the second yard of vinyl that I'd bought and did it again.
It's far from perfect but it's a big improvement over the horrible tape job, and really didn't cost that much.
My advice for anyone doing this: when tacking in the vinyl, don't worry about getting it perfect and wrinkle free immediately. I had to keep circling around the piece and incrementally stretch the vinyl and pull out any wrinkles. This meant I had to keep pulling staples I'd already put in, pull out slack, then restaple.
Also, it would be good to have an upholstering stapler for this project. The staple gun I used worked well enough, but wasn't able to drive staples in the narrow or tight spots.