You can buy a paperback copy (the very same imprint as the one I own) of Religio Medici here: http://www.amazon.com/Religio-Medici-Hydriotaphia-Classic-Reprint/dp/1440061238/ref=sr_1_13?ie=UTF8&qid=1326266180&sr=8-13
And here you can download an eBook edition for cheap (although the misspelling of the author's name raises my eyebrow a bit): http://www.amazon.com/Religio-Medici-ebook/dp/B004IAS15O/ref=sr_1_2?s=digital-text&ie=UTF8&qid=1326266304&sr=1-2