There are lots of options in the $15 to $25 range, including the CS knives mentioned above, the larger Hibbens, of course the old standby "blazing arrow". Jon Goss's "Dragon Knives", IMHO the best production thrower since the larger Blackjack, maybe better, is only $29 I think...
Remember you should get a small set at least so you don't have to retrieve your knife after every throw. If you only get one knife, learning is a lot harder. 3 is a good minimum.
There are even custom throwers in the lower end of the price range. Lee Fugat makes his "bare essential" model in the $15 or $20 range, and I think Bobby Branton also has his "sticker" in this range, so there really are lots of options.
You can find links to all the knives above at various throwing weapon web pages. <a href="http://www.sonic.net/~quine/thrower.html"> I have one here </a> which has a link to many of the production and custom throwing knife makers. Just read over the page a bit and you'll find the right links. There are other references linked there as well.
[This message has been edited by matthew rapaport (edited 08-17-2000).]