There's an old saying. "It's only worth what someone is willing to pay for it".
You know what you can afford, make him an offer.
I would be in the $10,000.00 to $12,000.00 range, with the understanding that you have only shown me three pictures. I am also uncomfortable with your description on condition.
There are a number of Model A Fords around, but quite a few of them are 20 or 30 footers.
Look at all the running gear, put it up in the air and check things out. Front end, springs, correct shocks, brakes and brake rods. New correct radiator and water pump, wiring, check as much as you can.
Now you will either have more questions or you will be comfortable making an offer.