Depending on where you live, certain Wal*Marts (not all Wal*Marts sell firearms) have the best price on Remington 870's. Remington 870's are legendary, I own 2 of them. I have owned my since the eighties. Never have had a problem with my Rem 870's: they've been in the rain, dropped in mud, slide down embankments, etc.
If you want to spend a little more check out Winchester's 1300 series shotguns. They have a smooth action allowing the user to cycle the pump very fast. They have the fastest pump action of any shotgun I have used.