I did mine myself, and admit that they're not perfect - however, my car is not perfect, either.
I would say it depends on how mechanically inclined, determined, and how much time you have to dedicate to the project. If you've never done upholstery before, you'll develop a whole new appreciation for those who do. It's tough, can be very challenging, and even a little unforgiving at times - but you'll definitely feel the 'job well done' satisfaction afterglow once completed.
As for what it costs to have someone else do it, you'll need call around. What's reasonable for some places might be ridiculously cheap or expensive for others. I know (based on other projects I've seen done for others) that paying someone to do it for me would've cost more than the materials I bought from TMI Products via CJPP (and that would be in the 'ridiculously expensive' category for most people who have more competitors available locally).
Then again, I expected to get raped based on my own experience getting a simple 'street bike' motorcycle seat recovered, which wound up costing me $300. :whistling: