Check out the link below for a little more info on Funks. Before buying, make sure it has the original Funk parts, such as cast starter nose, radiator, governor mount and pulley, carburetor "cap", and hood adapter. These parts are hard or impossible to come by, and would give you reason to dicker on price if it is not completely original. Engine parts are the same as Ford cars and trucks of the late '40's and early '50's, so getting parts for it should not be a big issue.
I wouldn't go any higher on price, and would try to get him down to around $3000 if you can. I would think $3500 would be top price for an unrestored Funk, unless it is in excellent shape. Good Luck.