Just to be clear, i7 builds tend to start at around $1400 or $1500 for gaming machines (and even then, you'd be able to get a better gaming machine sticking with i5 or AMD). You can get them at around $1000 or so if you never intend to play anything more advanced than Minesweeper/Solitaire. There's also no benefit to going with an i7 if you only intend to game...where those processors shine is serious editing and/or number-crunching.
And there's no benefit to going with multiple graphics cards if there's a better single card at your price point. Some games don't handle multiple cards at all, some games handle them ok, but as a general rule, 2 cards aren't going to scale 100%. It's typically more like a 60-70% increase in graphics muscle when you go from 1 card to two.