I've seen upped PMR's 7/8's fo for £100-£120. Realistically, I guess I'd be looking to pay a Maximum of maybe £150-£180 for an upped PMR 9; certainly less for one without any extras.
PM9 - Probably £250-£300
The prices depend on a) how much a seller wants to sell but especially b) what buyers are out there....with money.