Most gaming cards are geared toward 3D acceleration and even the cheaper ones have quite reasonable 2D performance.
You haven't really said what you're doing with so many monitors and what level of performance you need.
Many cheaper cards these days are quite reasonable in performance. Mine was very cheap and is dual head. They don't make them anymore though. That being said, it drives 2 x 22" monitors just fine. I'd class it as a $50 card now.
I have a colleage who has 3 high end gaming cards in the one machine. The problem he has is twofold. Heat, and power. He actually needs a 4th card in there, but the power supply can't supply enough power for the 4th. His supply is at 1.5KW already. Heat is a problem because there isn't enough space between the cards to allow the airflow to cool them properly.
So, go with a lower end cards and be aware of cooling. Unless you really need lots of performance like my colleague does you'll be in for a much more powerful motherboard too.
EDIT: Another option is something like this:
It really depends on your budget. The beauty of that is it's not going to use up all your PCI-express slots. Make sure you've got a descent power supply large enough to keep everything powered optimally though.
A few years ago, another colleague was given a high end graphics card by the boss who found it didn't fit his machine. My colleague ended up having to upgrade the motherboard, ram, power supply etc... all to get the card to run. So, watch out for that.