Mossburg 500, or if you can afford it, a 590. Low to high $200's.

For a rifle, Yugo and Albanian SKS's are cheap now. Around $90-150 depending on condition, they work, but are too long for inside-the-house work.

For a pistol, look for a CZ-52. Buy an aftermarket steel firing pin for it and it'll last forever. They run $100-125 in the surplus market, and 7.62x25mm (.30 Mauser) is availible in good quantity now.

My home defense weapon is a Mk.II, a civilian AK-74 clone. It's the smallest firearm I have.

spankaveli: that second one you posted is probably classified as an NFA AOW (National Firearms Act, Any Other Weapon), with takes hella paperwork for a civilian to buy.