I've only bought one ready-made gun rag in the past 12 years and that was because I left the house without one of my normal rags a few years back and didn't find out till i was an hour from home.
The rags I've been using for that period, were made from a 2yrd piece of "medium-weight 100% cotton broadcloth" I found in the "bargain bin" at the local craft/fabric store. each has lasted an average of 2 years (12 years, I'm on the last of 6), they're cut and sewn like a 20" square napkin, then I soak em in Hoppe's gun oil before first use and after a washing (if one becomes to crudded up with powder residue etc), between washings I re-wet if needed.
I replace then when they become too ragged after a wash to use.
I've also seen cotton "mattress/pillow ticking" (the blue and white striped stuff alot of muzzle stuffer guys use for patches) used for wipe rags.