The model number of the Yugo AK shown in your pictures in an M70AB2 (underfolder)....the M70AB1 is the version with the fixed wooden stock....in case you want to do a search online for relative pricing...
You really need a few more details about the rifle before anyone can give you an accurate value. How many rounds have been fired through the rifle etc? This would be an important question to ask your friend, unless you know that he purchased it in the very near past (since most if not all new Century built Yugo M70s come with plastic handguards, I'm going to guess that it was not purchased in the last couple of months...but I could be wrong). Has he had any problems with it...? Sounds like a fair price if it doesn't have too many shots fired (<500 or so), and if it's been functioning fine. The Yugos are fairly nice AKs.