I'm not familiar with the market, but a cylinder piston combo with all the work ready to go has got to be £300+. Any more than that then I wouldn't understand why someone wouldn't go for a brand new Athena 125 kit, or a little extra for the 170 kit.
The Zeeltronic, new they're around £240, so with the programmer I'd say £160ish is what I'd pay, otherwise I'd just go new.
Hope that helps.