In rural Sweden - where I now live - they're free when you find them in the ditch, notify the police about your find with identifying data like frame number etc and wait for 3 months. Assuming that the bike does not have a label identifying the owner - in which case you should contact him/her - they'll send you a letter confirming you're now the owner. Those bikes often need some work - how does a 30-speed MTB end up chainless in a ditch in the middle of nowhere? - but that is all part of the 'game'. It is hard to get closer to re-use, reduce, re-cycle than cycling on re-used bikes.