Brand new Console: I think they retail at about £90-£99
Used Console: Your looking at £50-£60ish for standard console. (Would expect wires and atlease one contoller)
Chipped Console: Add £20-30 depending on which chip or mod it has... (Do research on modchips as some cost as little as £7+)
Softmodded Console: Same as standard console as it dont cost to softmod a console although £5 extra for the effort could be a reasonable good will gesture.
Faulty Console: £20-£50 depending on the fault (always check error codes)
Yep add £20-£30 to the cost of a standard or used console. Depending on the chip and any other mods.
Never pay for amount of software installed, iv seen people trying to get more money for having stuff like XBMC installed which is freely available on the internet...