I think my friend paid £35 for his to be done and I must say it was money well spent. They looked brand new

The good thing is now so many people are doing this kind of work so they undercut each other so you can end up with a fairly decent price.
And like the picture in Guys post you'd be surprised the amount of dirt that your seats hold and lets face it, no matter how much shampoo you put on and how hard you scrub you dont get that kind of results!
Yeah ill definately be getting mine professionally done.