I think that one of the big sources of bearings were automobile front wheel bearings. Those bearings are designed for preloading of the bearings and the price on them should be in the $20-40 price range each which is pretty cheap for a bearing or that size. I would probably use a ball bearing (used until the '60s) for the lower resistance to movement. Unfortunately, I can't give you a particular number for a bearing but if you go down to a good auto parts supplier, you can probably get them to bring out some bearings so you can measure them. I'd get a bearing that I'd have to make a collar to hold the bearing tight. You will also want to make the bearing have a bit of preload so that it doesn't wobble about.