Sure! Hard to find one in the city but do some trveling and look for the public ones in the major onsen town or the ones in the wild. Based on my experience, I think onsens are cheaper the better in quality! If you want to do many free onsening somewhere near Tokyo, I would recommend Kusatsu Onsen(Gunma Prefecture). If you want to get serious about onsen, head off to Beppu(Oita Prefecture). I want to spend about a week there and just concentrate on soaking!!