Windows 7 - 3 Monitor setup with Nvidia GT 240 + ?

Hi I have an ASUS P6T SE motherboard with an NVIDIA GeForce GT 240 graphics card (512MB) already installed. I would like to connect 3 monitors to my PC but apparently the card only supports two concurrent ones.

I use my PC mainly for web design and development, plus recreation such as watching movies, however I don't use it for gaming.

Monitor sizes and inputs they support
17 inch: VGA
24 inch monitor: HDMI/VGA
23 inch: DVI/VGA

What is the best option for me to add the 3rd monitor?
My main consideration is price, I don't want to spend too much money just for adding another monitor to my setup. My PC runs pretty quietly now and I want it to remain like that, so noisy cards are a big no for me.
I've read about USB to DVI adapters but it seems they are not so powerful as proper graphics cards.
The other option would be to add another card to my existing one, something basic that can run my third monitor. I'm not sure if this is at all possible, and what cards you suggest.
And the 3rd option would be to take out my card and replace it with an ATI card that supports 3 outputs out of the box.

Are there any more options? And what do you recommend? Thanks.

Best option would be something like this,

Newegg.com - ASUS EN210 SILENT/DI/1GD3/V2(LP) GeForce 210 1GB 64-bit DDR3 PCI Express 2.0 x16 Low Profile Ready Video Card

extremely low power, silent due to no fan, and will fit no problem seeing as your motherboard has couple of extra PCI-E x16 slots. And you shouldn't run into any driver issues as it uses the same driver as your current card.

Thanks would any of the following be equal, as they are available from a nearby shop?

POV VGA CARD GF210 1GB (LOW PROFILE)
GAINWARD 512MB GF210 VGA PCI EXPRESS
GAINWARD 1GB GF210 CUDA - PCI EXPRESS

They're all the same spec-wise, just different manufacturers. Just pick the one that is the cheapest.