You could get the Remington 870 with the 18" barrel and 4 round mag tube. I bought mine this summer for about $360 total. And now looking at it, it looks like price has gone down some. If I ever want to go shoot skeet, I just borrow my dad's 26" 870 barrel. Having the ability to change barrels would be perfect for you.
I also strongly recommend 00 Buck or #1 Buck for home defense. I have 5 3" magnum buckshot rounds ready to rumble. Image: http://www.budsgunshop.com/catalog/images/95549.jpg http://www.budsgunshop.com/catalog/product_info.php/cPath/37_64_991/products_id/95549/Remington+870+Express+Synthetic+12GA%2C+18+Inch%2C+Fixed+Cylinde