You cannot purchase Eagle. A basic subscription costs approximately $100 USD per year. Plus whatever portion of your soul you are selling to the 'cloud'.
Have not used Eagle for several years because its autorouter updates broke my DRC, and because ver 5 made KiCad usable and reliable, and because windoze was finally kicked to the curb at my house.
Professionally, prefer the Mentor stuff. Personally, prefer KiCad because it is easy to force it to do things my way by shoving a Python script into it.