I can't afford even the 99designs rates, so I created the logo for my startup -- http://stellient.com -- myself. I searched through http://www.istockphoto.com and found a nice clipart which I tweaked in Inkscape, combining it with a nice free font from FontSquirrel; and I couldn't design my way out of a wet paper bag.
That being said, great logo design needn't really be expensive: http://misipile.com has one of the best portfolios I've ever seen, and their rates are not much higher than the 99designs ones.
I hate to break this to you, but using art from iStockphoto as a logo is prohibited. From the license agreement:
"For greater certainty, the following are Prohibited Uses and you may not: ... 4. use any of the Content as part of a trade-mark, design-mark, trade-name, business name, service mark, or logo;"
That being said, great logo design needn't really be expensive: http://misipile.com has one of the best portfolios I've ever seen, and their rates are not much higher than the 99designs ones.