I'd be a bit careful with these guys. A pal of mine was offered £4200.00 for his Mini Cooper by them. He thought this seemed a bit low and looked around. Showed it to a few dealers and sold it to a garage for £5800.00 cash - no trade in. Bearing in mind they will put their mark up on that as well they both got a good deal.
Don't rush into anything - shop around.
No its not a fair price, best get intouch with autotrader, if you are after selling it private
they also tried to rip a mate of mine off, he wanted to sell his Merc, placed an ad in autotrader 2 weeks later he sold it and was 2.3k better off
Beware Webuyanycar. Firstly as you say they offer peanuts. Second if you take their offer up. They direct you to one of their agents. From my source it was Carcraft (or something like that) nr Lakeside, Essex.
Once there they go over your car and judge it by Rolls Royce Concours standards. Flyspeck here....dust there...those wheelnuts not in alignment etc. Then after making you wait about SIX hours offer you about 20 to 25% less than the previous offer to cover these imagined defects.
The staff get commission on the amount they 'save' by screwing you.
By this time (several hours) your tired, hungry maybe the kids are screaming and you just want out. So you take the derisory offer. Then there's the £149 fee (for something or other).
Either way ..it's a con.
Spend the £50 put it in Autotrader. If you can't be bothered use http://www.sure-sell.info/ Honest John from the Telegraph recommends them.