Have a look on autotrader.co.uk and do a search for cabriolets and convertibles to see what they are going for on there, as Vix says it all depends on a lot of things, but one thing you have going is that the weather is getting warmer and it's the right time to sell for the best price. My best guess would be around the ?1,400 to ?1,800 price range. Put a for sale sign in the window of the car and people will notice while you are driving round.