Rule out saltwater if youre only willing to pay 250 for one. That would probably buy you the tank, and maybe the stand. If you want bowfront, that just makes the tank cost more. You could get a 55 gallon standard kit for around 200 dollars The stand would be another 50-100. Then youll need about 40 dollars worth of gravel. Most kits dont include heaters, so thats another 30-40 dollars. Then the fish...
Fish tanks are expensive. If you want a somewhat large tank, your budget cant be small. 100-250 would set up a 20-30 gallon tank almost completely.
Then, if you want saltwater... Youll need alot of liverock that costs 5.99-6.99 a lb. Youll need a skimmer that costs around 100 dollars. If you want coral or anything like that, youll need a light setup that costs about 500 dollars for a 55 gallon.
If you think you can buy a saltwater setup for 250, you obviously havent been researching in the first place and everything would die. Oh, wait a moment. I just reread what you wrote, and apparently you already have something to put the tank on. But its very small. A 20 gallon tank is 24 inches long. Thats already too big for your little area. Between your budget and your area, Id say you can pass on a fishtank until you are actually ready for one. Or, at least wait until you realize a 10 gallon is about as large as you can get.