It's not $80 worse case scenario buy $8 of meds and treat it in your current set up. Hold off the Discus until your plec is better and then have a happy tank with discus and the plec. At least try your LFS. You say what's the difference between feeder fish and killing your plec... well someone may eat beef but it doesn't mean they have to kill a cow because it gets a toothache. It's just another wasted life.
Anyway not a lot I can say except RIP pleco
Anyway not a lot I can say except RIP pleco