I think you have been more than fair. I would tell him he has 30 days to come up with the three hundred. After that it is no longer for sale. Its some what a gamble be cause he could try and get the police to make you give it back. I would take that gamble and loose three hundred before I let him rip me out of 150, especially since you have been more than coopertive. He looks to be trying to take advantage of you. If it were mine I would be glad to be able to pay you for it, espacially this day and age hes lucky it was seen again, most things are not. Just my oppinion but youre rite it sucks getting the shaft for trying to help.
Brandon