First, you would need the tank. duh j/k.
At walmart you can get a 10 Gal starter kit for like 35 bucks.
It comes with a heater, HOB filter, 15 watt NO lighting, and the hood.
That what I have as a sitter (its been sitting with one damsel and a snail in it for 3 months) right now. Eventually it will become another nano reef. It works great at the moment, it's quiet, with the help of an extra PH it's got great flow. I have a CC substrate which is going to change to LS someday soon, and a small plenum, that is gonna take a hike I think.
I don't have a protein skimmer, but would certainly recommend one on a 10 gallon, just for safety sake.
Another road to turn down would be to buy just the tank and start with your own DIY puzzle on the equiptment.
Walmart sells just a 10 gallon glass for around 9 bucks. This way you can do whatever you want when it comes to flow, heating, and lighting without having to execute some perfectly good equiptment to make room for your preferred equipment.