for a 100 gallon reef tank, you will be spending a lot more than $600. If that is all you are looking to spend, consider doing a fish only tank, or if you're really not willing or able to go over that budget, fresh water. Salt water is an expensive hobby.
I don't know if you already got a 100 gallon tank, but equipment for that alone will tally higher than $600 (spefically, lighting, which may run you at least $300, depending on how in depth a reef you are doing). Then, comes the live rock expense. You will be spending at least $300-$400 on live rock in a 100 gallon, because for a reef, it is essential to have 1lb. of live rock per gallon. And that is the very minimum. Next, you will need to buy sand for your tank, a heater, two or three powerheads, RO water, and the other small essentials (such as calcium, essential elements, salt, etc). In reality, just to get a 100 gallon reef tank started, I'd say you are looking at least at a $1000-$1500 expense.
Don't get me wrong, I am not trying to discourage you. A 100 gallon tank for a reef is an excellent size. For a beginner, it really is the bigger the better (and easier to maintain water quality). I am just trying to warn you about the expenses of a saltwater tank before you get fully into the hobby.