I'd save your money and wait until you have a couple hundred more to play with. Right now, anything you get with your budget is likely going to be a disappointment.
And I wouldn't really worry about the whole frequency thing on some TVs. After 120Hz, which honestly I cannot see an appreciable difference on over 60Hz, they start using a bunch of funny math to reach numbers like 240Hz or even 480Hz, 640Hz, etc. They break the screen up into sections, and each section has a frequency of some Hz, then they add those up for a total of YHz which is what you see on the box. Even 120Hz sets aren't immune to a few little tricks to get that number.
What I would strongly suggest holding out for is LED backlighting. That can make a HUGE difference on image quality. You can control the backlighting of the entire screen much more precisely that way, giving the resulting image a much more natural appearance. If you want to get some idea of the difference, go to an electronics store that sells Apple computers. Start by looking at any random PC monitor which will likely be using CCFL backlighting, then go look at an iMac screen which has LED backlighting. The quality difference should be very noticeable.