The money is in the front axle only IMO. How long has it been sitting there? How desperate do you think he is to move it? I'd say I've got $800 and can haul it off today. When he comes back with $1000, I'd say all I have is $800.
What are the city codes as far as having something like that sit in your front yard. Be an anonymous neighbor and call in a complaint so he gets a letter from the city to move it or get fined.
Do that after he turns down your $800 but make sure he has your phone # to call you the day he gets the notice from the city.
If he isn't motivated to get rid of it, make him motivated to get rid of it.