Flightstick joysticks are what you want. They are perfect for this application. I would check EBay, that's where we got our 4, and I paid between 1 and 20 dollars per joystick. The best part about these is that they are ambidextrous.
http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW
We have a similar one to this, but ours don't have the thing on the top.