I made an offer on a 300D turbo diesel with 510k on the clock just over a year ago.
The thing was actually in great shape. He was trying to sell a rust bucket wagon with about 200k on it as well. I offered him $1k for both. I think he tried to get me up to $1500 so we did not make a deal.
$3k seems high to me. I would think under $2k would be more along the lines of the purchase. Realize you are most likely going to be putting money in to it to keep it running and if you don't do the work yourself you will end up paying way too much as opposed to buying a more expensive car with less miles.