I find that a glass 10
gal tank is most convenient because they're cheap and small enough to easily dose with meds if necessary. Secondhand or scratched up wouldn't matter. You could also use a clean (new) rubbermaid container, a 5
gal bucket, or a small plastic garbage can - so long as there is a lid to prevent jumpers. Any quarrantine tank is better than none.
My quarrantine tank has no gravel, rocks, plants, or light - it's a completely bare bones operation, which makes cleaning and disinfecting a breeze. It's also less expensive.
You would also need a heater (50W for a 10
gal) and a filter. I always have cycled sponge filters running on my other tanks for this purpose. A slightly more expensive option is to have a small spare
HOB running on one of your other tanks at all times - ready to be called into action when you need to set up the quarrantine tank.
Finally, you should have separate nets and water changing equipment for the quarrantine tank...otherwise, what's the point?