Depends on a lot of things...if it is a Hi-Power (P.35), if it is an early (stock attachment iron and adjustable sights), mid (adjustable sight) or late (no attachment, or adjustable sight) type.
Also, it could be a Browning Model 1922....
Hi-Powers can be up there in price I paid $550 for mine, and it is the late type (non-adjustable sights, no stock attachment piece)...the early ones can go $900 and up. Does it have a proper holster in good condition? Add another $125 or so....
Model 1922's run around $300 or so, again depending on type and whats with it. Also caliber dependant as these came in 7,65mm (.32) and 9mmK (.380). The 9mmK guns bring a bit of a premium.
My Model 1922 came from a family friend, his father got it from a Luft pilot after the surrender. It was a Dutch contract gun, captured and issued by the Germans, then captured by an American. It came in a Luft Theuermann or drop holster, with the capture papers. It is one of the coolest pieces in my collection.
If he is offering it to you, my advice is to take it with many thanks. He is probably happy it will be going to someone who will appreciate it.