Proud Texan, I am absolutely not flaming you but I think this needs to be pointed out.
As everybody has said, the cost of saltwater tanks is a lot higher than tropical or coldwater. It looks like you've done the same as me and saved up for ages to collect enough money. I'm 14 and like krib my parents won't pay for my fish obsession either.
But if you really are in your early teens like us, I think one of your main problems is going to be time. I think you've got brains - so if you want to do well in school, you have to put the time in. There are bad weeks when I struggle to keep on top of my commitments and still look after my fish tanks. The fish come first - they are living creatures and I will not neglect them because I'm busy - but I have cut it rather fine several times. Saltwater tanks need more monitoring, more time and more money put in than freshwater tanks do. A 75 gallon tank is enormous, and whether it's a fresh or salt water tank you have to make sure you've got time to maintain it.
Also, we are trying to help you. You've flamed me personally once (ignoring, by the way, most of what I had written) and I believe quite a few other people as well. We want to help people but nobody is too inclined to help somebody who goes off and flames us in other threads. Most of us know what we're doing. Those of us who don't are trying to learn (or else they're trolls).