Supercharged Opel Kadett........ my one, whats it worth ?

I suppose it's worth whatever somebody will pay. Forgetting how much you have invested it's basically an incomplete abandonded project. Have you discussed with the potential buyer how much they think it's worth ? They might look at it and value it differently to yourself so then it's negotiate.
Realistically you are going to be well "out of pocket" by selling now and even complete might struggle to break even. This is the penalty of our hobby - we play with the vehicles for enjoyment not to make money. After all just think how much people spend down the pub, takeaways, daily papers, fags, etc and yet have nothing to show for it at the end of the day whereas at least you can see where your money has gone.
Paul H