As others have said, R is open source and works fine for Mac. There's a learning curve if you don't have experience in computer programming. But I think there are some good GUIs out there like R Studio. And there's a massive amount of support in the R communities. Their Google group is massive.
I minored in stats in grad school, so I thought the courses on Coursera and EdX were nice refreshers. The basics of biostatistics need to be repeated until it's second nature. So, it doesn't hurt to take a couple online courses to learn the material from different directions. The online courses integrate basic stats with using R, so it might be perfect for your needs.