I dont balme you for wanting more, I would want more as well, but as it is thats just my guess as to what you would get. The bodywork alone must be worth £400 if you was to break it for parts. Get it going right and put MOT etc on it and it may fetch around £1800.
I just sold a very nice MC18 with a few running problems for £550, I wanted nearer £800 but that is all I got! It had extremely nice paint job on it and had very low miles. Problem is people wont pay a premium for a bike that is not running right and has no MOT.
Best thing to do is fix it up and keep it....you know you want to really!!!!