I've tried a few of the more inexpensive CFD programs for airfoil/wing work, and my opinion is they aren't there yet. Klugy, non-user friendly, and questionable results has been my experience so far.
There are some shareware. In my experience, I suggest AirfoilAnalysis shareware in versiontracker.com. Is the finest implementation of the Vortice Panel Method for windows and Mac I ever seen. Check it out. Obviously, it has all the assumptions and limitations of the Potencial Flow theory. That are low mach,incompressible,inviscid and steady flow.