Setting up a quarantine tank ...HELP....?

Your best bet is to go ahead and purchase a heater and small sponge filter. If you have multiple fish in the tank that have ich, slowly raise the water temperature to around84-86 degrees. Preferably over the period of a couple days. Add aquarium salt at approx 1 tsp per gallon. Keep the temperature up for a week or two. This shortens the life cycle of the ich and allows treatment without any medications. As far as the tank needing cycled, I keep a spare sponge filter in one of my tanks just for situations like this. You can treat the water, install the heater and the seeded filter and have an instant hospital/quarantine tank.