Foxit Reader
is free, the Editor has an evaluation version which can be upgraded on payment. Most websites just post a link to Adobe whenever they include PDF files. I don't see why you couldn't link to Foxit instead. Just put words to the effect that "If you don't have a PDF reader installed on your computer download one
here". If a Mod sees a problem with the legal aspect of this please edit as needed.
Unfortunately it doesn't look as if they do a version for Mac's.