That would be hard to quantify as there's much more to do than you would ever imagine, my Mondeo is a proper finished product and to get it to that stage takes time (expensive hours) but drive in drive out I reckon you would be spending 10k ... Sounds like a lot of money but the end result is a really stiff chassis that's way better than a Sapphire... Wheelbase is longer too.

Btw I'm not interested in doing the conversion, I'd rather have the only Mondeo Cosworth !

I understand your problem A rwd Mondeo would be a far better machine than a Sapphire so you know what you have to do....