edit... I didn't notice suzieh's reply since I was sidetracked a bit while typing, but her advise is good. I'll leave my post as is anyway.
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Well, you will not find much at all for less than $500. I would recommend you save up for a better cutter, however in the interest of helping you out a bit, you are probably going to be looking into a Stika in order to stay around that price. Here is a link for information. It's still a little more than $500 and by the time you add tax and shipping..... You can probably find one on eBay for less.
http://www.stika.com/
Stika's parent company is Roland, and Roland does make some better cutters. This at least means that they know something about making cutters, and I would guess that the Stika is the best cheapy cutter on the market. I still would not really recommend one of these though. Many people are happy with them though.
Probably one of the best sites to learn all about cutters, also called plotters, and how to use them is over at signs101.com . It is a site for learning how to make signs mostly, and that is basically what you are doing with a cutter for making t-shirts. It's the same exact process, except for two things.
1. you are using a different kind of vinyl for t-shirts
2. you are cutting your design in mirror image, or reversed.
Even though most of those guys do signs, many of them also do t-shirts.