I'd say about £2k for the boat, same or a bit more for the outboard, Trailer could be as little as £250 for a Chinese jobby, but may be a better one. Console, steering kit and fitting £500- £800 depending on who does it.
So I reckon the new cost is about the same as he's asking for a 2 yr old boat, and i'd expect a discount of at least 30% off the new cost, probably more.