608 bearings are really cheap by bearing standards. For instance, you can get a pack of 30 608ZZ bearings on ebay for only $15 shipped (from China, of course). That's only $0.50 per bearing!
The spool holders I've seen so far either don't have a foot I like, don't use the type of rod I want, or don't use the size of bearing I have on hand. This thing fixes these things for me and if it does so for you, too, great!
I've included the OpenSCAD source and the compiled STL file.
You're going to need 4 x 8 mm or 5/16 in. threaded rods of lengths useful for your spool. You're also going to need 4 608 bearings. Use 8 mm or 5/16 in. nuts (depending on which threaded rod you used) to secure enerything.
Print out four of the feet, then assemble in a way that makes sense for your specific filament spool.