I charge anywhere from $350-$800 (corporate package). You get what you pay for. I spend a lot more time than 10 minutes on a logo, and that looks like what the people spend that are making them for $10-$20.

If you're wanting to expand your portfolio then look up a charity, church or a non profit site and help them out for free. That's what I did starting out.
Cheap selling your work only devalues the profession. And if your logos are only worth $10-$20 maybe find a different profession.