My quarantine tank (QT) is a simple box of water. Made of acrylic, it holds about 12g of water. I use a small 50w heater, a LED light, and a Vortech MP10 for flow. Some dedicated live rock and some PVC fittings complete the system. Stick a glass thermometer in the tank to verify your target temperature is consistent.
PVC fittings gives the fish a place to retreat to if aggression takes place. Daily water changes keep the water parameters in check, taking water from my reef to refill the QT, and then adding new saltwater to my reef.
I use this tank to house new arrivals, whether they are fish or corals. Fish stay in QT for a few weeks to make sure they are healthy and eating. Corals are treated with Interceptor (for Red Bugs) and then are later dipped prior to being placed in my reef tank.
If a powerhead or Vortech pump isn't available, an airpump and air stone will do the job adequately.
The quarantine tank is always running so it is ready to use at a moment's notice. If you want to set up a high-end QT, consider getting a controller that will regulate the light periods, run the heater and cooling fans, and even top off evaporation needs. The more stable the system, the better it is on the livestock. You shouldn't need to dose anything if you do water changes frequently, and corals can survive a few days without intense lighting. You don't need expensive lighting for the QT.
Learn more about Quarantining and Dip procedures with this article.