http://www.mossberg.com/pcatalog/Price590.htm [51663 MSRP $531]You might also try Arizona Gun Runnershttp://www.kyimports.com/rifle3.htm#Mossberg [51663 @ $389.99]
http://www.arizonagunrunners.com/Products/Mossbergshotguns/mossbergshotguns1/mossbergshotguns1.html [51663 @ $360.00]but they're harder to get ahold of - they don't answer the phone - and you have to play phone tag, or email tag, if you want to buy something from them.
In combination with the Federal Classic F131RS rifled slug, at 3110 FPS muzzle energy
http://www.federalcartridge.com/cgi-bin/specs2.pl?product=31crsthis should stop all but the worst of the bad guys.
Federal
Load #Energy in Foot-Pounds
(to nearest 5 foot-pounds)Muzzle 25
Yds.50
Yds.75
Yds.100
Yds.F131RS 3110 2555 2120 1785 1540 F130RS 2805 2310 1930 1645 1450 F127RS 2520 2075 1725 1455 1255
The great thing about long guns is that there's no waiting period whatsoever.
While there may be no federal waiting period for long guns, your state may have one.
If I'm not mistaken, California's waiting period is five days for long guns and ten for handguns. (I could be wrong on this; I haven't made a purchase lately.)