What does an aquarium cost?

It can cost hundreds or thousands of dollars, depending on what you want. My best advice is to use Craigslist to find a used tank online. If you can find an already established tank that would be best because then you have all the equipment and the fish, and even if you don't like the fish, you could probably get some different fish by trading them in at a pet store (you'll probably have better luck and advice from a locally owned one rather than a petco or something.) there will be a couple extra cost involved, like a good number of 5 gallon buckets to help transport the contents, fish, and at least 50% of the water, and it will take a couple of hours to take down the tank and prepare everything to transport, but the owner could help you with that. I've found a 55 gallon full set up with fish for $150, about the cost of a NEW 55 gallon tank alone, w/o a stand or anything.