I would recommend getting on Craigslist and finding someone’s old freshwater setup with HOB filter, heater, air pump, and canopy (usually pretty cheap). I would shoot for a 20G
Once you have that get a small bottle of copper power, sea chem ammonia alert badge, some pvc fittings, and a filter sponge with a bottle of biospira or fritz9000 (bacteria in the bottle)
Setup the tank and get it up to temp put the sponge in the HOB with the biospira.
Get the fish netted and into the QT and start dosing copper, having 20G 4ml of Copper Power should get you right around .52ppm. I would dose 4ml immediately and then tonight another 2ml and 2ml 12 hours later and keep doing this until reach therapeutic levels (1.50ppm). You want to test your copper levels with a test kit and since this is ich and a Benny is shoot for 1.75ppm (this gives you some wiggle room above therapeutic levels). You’ll need to maintain 1.75ppm for 30 days straight to cure the fish. You will need to leave your main tank fallow for 76 days to eradicate ich from the tank.
If it’s in your budget I’d strongly recommend the Hanna high range copper checker and an extra box of reagents from BRS.