Its not that hard to do, nor is it expensive to quarantine if you work it out vs. the cost and time of having a sick tank. Heck, a rubbermaid tub, some PVC pieces, dead rock, heater and an elcheapo HOB filter are all you need. As far as having one cycled, that's not really needed if you have another display tank up and running [note: that tank must be disease free :lol: ]
I used to always have fresh saltwater mixed and ready, and if I decided to buy a new fish I'd setup the Q tank using water from my display tank. Then, I'd just put fresh saltwater in the display. I had a 10 gallon tank lying around just for that reason. Everyday I'd change add freshwater to the Q tank, pull out maybe 3 gallons and replace it with 3 from the display... you get the idea. That's an easy way to keep the water quality good. In a few weeks, the Q tank cycles and I then backed off on the daily change.