Before you even consider getting a tank, first go to a book store or library and get some beginner's aquarium keeping books. Most of the better ones will walk you through selecting your equipment, setting up and cycling your tank, and properly maintaining it. Knowledge is essential if you want to be successful at this, there is much you need to know.
For a tropical tank, you NEED a heater, in addition to the filter, hood, and gravel. Your aunt probably has a canister filter. Not necessary, but the best type there is. A Hang-On-Back (HOB) filter is perfectly adequate, however. The "bunch of cords" go to the heater and lights.
If you are determined to buy new, you could wait for Petco to have it's "dollar a gallon" tank sale. That way, you would only have to pay $55 for the tank. Be aware that they mark up everything that goes with it! You must have a stand. A filled 55 gallon, completely set up, will weigh around 500 pounds. Expect to spend several hundred dollars to get completely set up. Nobody can give you exact figures, it depends where you buy things from.
I wouldn't be adverse to buying used, mine was actually given to me! It works and looks just fine. I see them all the time on a local classified ad site for as little as $100. I belong to local facebook yard sale sites, and just saw a beautiful stand for a 55 gallon, for $20! If I had a use for it, I'd be on that like white on rice.
One last tip: do not seek advice from employees in places like Petsmart, Petco, etc. More often than not, they know less than you do about the subject. Try to locate a locally owned and operated fish specialty store in your area. That is where you will find employees who know what they're talking about. Good luck!
Hobbyist for many years.