Hi Swissrose - here in South Carolina you can pick up a new Remington 870 Youth in 20 guage for about $250.00 or so. "As is" the gun is fine for home defense. The other option is to look at used guns. I don't particularly support the "Mart" stores but you should be able to special order one from Wal-Mart.
Most important thing to do is get several boxes of the cheap field loads and practice.
Please wear eye and ear protection when ever you shoot!!
"Hear the voices in my head, swear to God it sounds like
they're snoring." -Harvey Danger, "Flagpole Sitta"