Drillspot has what seems to be the lowest prices on Flex-Hones. For instance, $8.97 for a 1/4″ hone and 12.01 for a 3/4″ diameter hone. Of course, they do have many different sizes available — this one just jumped out at us.
Flex hones are used to debur and smooth a bore, as well as provide a cross-hatched finish, which is important for retaining lubricant on the walls of a cylinder (oddly enough you don’t want a polished bore in many applications, you want a bit of tooth) such as a brake cylinder. Because the individual “globules” of abrasive float in their bristles, you get a self-centering action that should give a uniform finish.
Flex Hone [drillspot.com]