Bit tough in some ways as they could be good quality tools or just cheap tools, see what the make is and go do a google search for there prices, or to one of the craft supply houses.
Try and get the guy to give you an idea of how much he wants, the point is you want them as cheap as pos.
Its hard to say as you give no sizes, and turning chisels can go up in price with size, and quality of meterial.
You can get a set of cheap turning tools from machine tool and ebay for £10.00 so there is no knowing what the tools are you are on about.
If there not the cheap chisels then offer him 10 see where it goes. LB..