Ortofon OM5.
If you like Ortofon try the M20 FL SUPER that was one of the cheapest among cartridges of the month in MM thread on a'gon years ago. I don't have a cartridge anymore, a friend is happy with it, but i still have NOS nude Fine Line stylus for it. Cartridge generator without stylus is cheap.
Another killer option for you could be Stanton and Pickering cartridges like 881s mkII or XSV3000 , both with nude Stereohedron diamonds like this.
Don't know what's your limit to call it cheap, normally under $350 is cheap for a decent MM. Glanz moving flux cartridges often on ebay for under $450 (the best of them is 610LX). But if you're in the States then definitely look for Stanton 881 or 981 (or Pickering XSV3000 or higher).
P.S. When you retip the ART-9 with SS it is no longer ART-9.
He could upgrade Denon 103 with his best diamonds and/or cantilever, but the ART-9 is not the case.