It all depends on the condition, if they are perfect then you can basically name your price within reason but if untested then it's basically how much someone is prepared to risk on taking them off you
PM sent with my 'personalised offer calculator' :D
I wish I'm not that stingy, even thou I should be but their is always a limit when comparing the costs to that of switching over to MPI and it's various benefits and having to weigh them all up isn't actually as easy as it seems, it's like trying to decide to improve the Starion engine or throw it out and stick the DOHC one in etc