How many did you have in mind? Two large monitors just get plugged in, and you can buy a stand. Four monitors might involve changing/adding a graphics card. You will pay 2-4X retail if you purchase from a "muilti-monitor vendor". There are many threads on here and a few knowledgeable posters here than can save you dough.
If you give us your system specs we can tell you what kind of video cards you can use & how many of them. Then you can find some good monitors on the cheap and a multi stand too. To go to those companies that "specialize" in multi monitors is tremendously inequitable.
Dell and Thenerds.net sell numerous makes and styles of multi monitor stands. I bought 2 quad stands from nerds a few months ago. You can expect to get some of the best prices thru them. example: thenerds.net has a quad stand: Ergotron DS100 for $274.00 ..............not including monitors http://accessories.us.dell.com/sna/category.aspx?c=us&l=en&s=bsd&cs=04&category_id=5387&~ck=bt&p=2 http://www.thenerds.net/Computer_Monitors_Monitor_Stands_Search.html
Here is what I don't understand... Why would I want to buy a "quad-monitor stand", which stands on 2 pedestals, instead of using the pedestals that come with the LCD monitors? (Though I would have 4 pedestals) Spending an extra $500? Answer: To look neat. (Oh yeah, I always forgot...)
Custom stands are easy to make if you have the means to do so. They can be made out of wood or metal. The monitor manuf's tell you what size & thread bolts you need. All you need to do is determine the length of the bolts based on the material you use.
yeah, you can get some 1/2" water-pipe from Home Depot and weld/braze your own brackets for monitors.
Stacked Monitor Stands - www.multimonitormounts.com is where I got mine for 4 or 6 - the 8 is really 2 4 mounts together
www.multi-monitors.com or www.digitaltigers.com as both have a good array of choices. IF you are handy, I like the Home Depot idea.