I have seen them for sale from $500, to over $1200. There is a Browning Auto 5 in 90% condition for sale on gunbroker right now for only $600. Browning Auto-5 Shotgun A-5 - USED 90% Condition : Semi Auto Shotguns at GunBroker.com
I don't know what year it is though. If your friend doesn't want to pay that much for one, you can get a old Remington model 11 for about $350. It is pretty much the same gun, just a different name.
Here are some pics. The first one is a Browning Auto 5, the second one is a Remingtone Model 11.