Throw the money in his face and do the only hand to hand combat I'm fully comfortable with. A face to face krav maga gun disarm technique you can find in videos. I may not even get the gun away but the first move points it away and pins it to his body...I'd draw and fire.
If I'm down and bleeding, I'm in trouble because my gun is on the dominant side, and I'm down and wounded. I want to say I would try something, but I may give him what he wants and hope he leaves me alone. Sounds very sheepish, but he obviously knows a few things to hit my dominant arm, and I'm in a very bad way on the ground arm wounded, waay to slow to draw and not much for a fight.
Gotta trap his gunhand to have a chance. I would try to put myself in position to do that, trying to mask my movements as things I was doing to try to reach my wallet with my non-dominant arm.