You have a few options... Scenario 1
You could get a video card with as many connectors as you need off the back but will also require 2 DVI to HDMI adapters:http://www.newegg.com/Product/Product.aspx?Item=N82E16814102938&Tpk=5770%20flex
and you will need to purchase an additional DVI to HDMI converter cable:http://www.newegg.com/Product/Product.aspx?Item=N82E16882379069
This setup would cost around $150. I only worry about how much space you have in that case. Do you have room to install a two slot video card in that case?
With that setup you could plug hdmi to one and DVI to HDMI to the other two, though sound will not travel to the monitors connected through the DVItoHDMI connection.Scenario 2
You can get a good cheap video card with HDMI out and use the $110 splitter I mentioned earlier:
Also around $150. The advantage with scenario 2 is you also carry audio to each display in addition to being able to move the splitter to other PCs.
Additionally, with both scenarios you have to buy HDMI cables. There's a company called parts-express.com that carries tons of these cables at great prices.