At a minimum, I'd go with a Marlin XL7 or XS7 that's in the $300 range or so. Then I'd top it with a Nikon Pro Staff 3-9x40 scope, that you can buy on E-Bay for $100-$110 new. Good rings and bases will cost you $40-$50. That combo, in my opinion, will last you a lifetime and would be a great gun to start with.

Don't rush into things, and keep an eye out for a good used gun -- you'll get a lot more for you money. Like another poster said, don't go too cheap -- you'll regret it. If you must save your money a little longer for a good gun combo, shoot Federal Tru Ball Slugs through your shotgun this fall. I use them in my 870 and they are very accurate out to 50 yards with a vent rib barrel, which is adequate for the woods hunting I do in Michigan.