I wouldn't give him a cent after the way you've been treated Gurms. If you do, stick to what you've offered and if he doesn't think it's enough, he'll just have to suck it up.
There's an old saying isn't there that when someone shows you who they really are, believe them. Well I know he's your son but he has shown you who he really is and if you agree to this reconciliation, he'll revert back to the person he's been up until now.
As sodapop's posted he's using your GC as a bargaining chip, which only goes to show just how unpleasant he's prepared to be.