As in anything else in this hobby, you get what you pay for. That is not to say you can not find a decent fixture in your price range, but too many times I have seen (and been victim to) people saying, "Man, I wish I would have bought the nicer one from the start" rather than buying a "cheap" fixture only to find out that it isn't sufficient for what they want it to do.
Wuton is right in saying that you can find a deal in the selling forums from time to time.
I wouldn't necessarily agree that halides are a ton more expensive than t-5s. It depends how many bulbs we are talking, frequency of use, electricity rates, etc. IME, the fixtures you are going to be able to find in your price range probably aren't going to be the most energy efficient fixtures.
Ask yourself this, what exactly do you want your lights to accomplish? What corals would you like to keep? How much are you willing to spend annually to change bulbs? What is more important to you: growth, color, both? Do you have a canopy to hide retrofits (which are generally less expensive)?
For what it is worth, I have an 8 bulb Tek fixture on my 48" tank and I can pretty much grow anything under it. It is by no means top of the line in terms of t5's, but it is a quality fixture. If you can find one for around $200 or so, I'd say bite the bullet on the extra $50.
Hope that helps a bit,
Ryan