Actually, you don't need to buy Xcode4 just to get gcc ;) Just have a look at the opensource page of apple: http://www.opensource.apple.com/source/gcc/. You can get all the sources you need and thus could also create your own "brew package", or am I missing something here?

Also you can still ask your users to find their OSX-DVDs and install (though an older version of) Xcode from there.

If someone already mentioned the above, I apologize, but I'm too lazy to read 220+ comments :P