You can make a four player game of Pit out of a standard deck of cards by removing the aces and the face cards (or the 10's and face cards. Either way, just so long as you have only nine cards in each suit.) Then you try to collect suits (instead of commodities) in order to win. You can also vary the values of each suit, just like the commodities are of varying value in Pit.
I've played with 2 normal decks. The object is to corner all 8 cards of a number. This is only 1 less than the 9 needed in Pit (if I'm remembering right.) It worked well.
In fact, the advantage for me was that I played this with a kid's group and they get pretty rough with the cards. So, rather than worrying that my Pit cards may get wrecked, we all enjoyed a wild time with the old cards.