$70 is probably fair for a friend in its working condition. Replacing belts can take a hour or two, plus the cost of the belts. A Marantz collector would pay that much for just a mint woodcase. I got my 5025B with shipping for about $50. I had to fix it and it works great now.
Best thing to do is give your friend as much information and let him decide what he wants to pay. Then go from there.