Sounds reasonable to me. Offer what you think won't offend him. I usually shoot for 60% of the asking price. Bring cash, put that offer in one pocket and the rest in the other.
When you go to make your offer pull it out and say I'll give you $600 and show it to him. When they counter, which they usually will, review all the problems and how much your going to have spend. Then wait, re-look over the car again and then counter his offer with your next.
If he takes the $600, you know you should have offered $400.
My last car I bought for 1K with a 2K asking price. Sometimes it works other times it doesn't.
I think I get just as much of enjoyment out of the purchase as I do the car itself. It's a game. To me most of the stuff I buy I don't need so I have no problem walking away. If it's not advertised sometimes it's the best bet to walk away and come back later.