You have the idea. Bargain. If the seller has the feeling that you will walk away from it you're in a much stronger position.
FWIW, years ago I had a cousin that really tough. When he found something he wanted to buy in the newspaper, he decided
how much he would pay and that's the money he would put in his front pocket. small denominations so the bankroll would look very tempting.
Unless the seller is married to the equipment, the idea of cash in hand is a very powerful tool.
Personally I'd aim for the three hundred mark. 340 likely to be tops.