I have been lucky enough to get two projects for free.  They have both needed lots of love and some new parts.  Petcocks always seem to be crap, carbs always need work.  I also have learned that it is smarter to have a pro do the fork seals and to expect to buy new tires.  $600 is my base expectation when restoring an old bike.  But, that's cheaper than buying a running one and it is fun to piece these things back together.  I hope a GS500 comes my way again.  I loved my old one.  It was developing potential engine problems and I don't play in there....  yet...