A ten gallon with bare minimum will do fine. They aren't going to be living in it long enough to need any more than the basics.
Heater, saltwater, a cheap hang on back filter, and a small power head,like a 20 dollar maxi jet or something to add circulation. Add some PVC pipes for the fish to hide in, and that should be plenty.
Some people quarantine w/out any filter. They simply change the water whenever they put in a new fish. I wouldn't, spend the extra 30 bucks on a cheap filter.
The fish is going to be in there about 10-14 days typicly, not really enough time for one fish to sweat and deficate in a 10 gal tank, or at elast enough to enough to cause pollution, and eventually its own demise. Your simply checking to see if anything was carried in with it, that should show within the first week.
Just make sure they are as stress free as possible, hiding places are a must.