Here is the list of basic (must have) items you need in order to run a tropical fish tank.
Fish tank,
Filter system,
Heater,
Air pump,
thermometer,
water conditioner,
fish food,
The other things you need for tank maintenance,
aquarium vacuum,
fish net,
two 5 gallon bucket,
algae scraper.
More items which are not must have but they are good to have.
Substrate,
tank cover/hood,
Lights,
decoration.
You would really be looking at beyond your maximum budget of $200~300, and since you want a hexagon shaped tank, your best bet is to get a used one from ebay for cheap. A 50 gallon might also be out of your budget.
Check out the prices of these hexago shaped fish tanks from Petsmart.
It is also recommended to use a real fish stand instead of other furniture which are not designed to hold heavy weight. A 50 gallon tank filled with water, equipment, substrate could weight well over 400~500lbs.
I also wouldn't recommend saltwater fish for beginners. They are more expensive to have, harder to maintain.
Are you willing to scale down on the tank size or do you wish to raise your budget limit?
