Official digital versions are updated with the latest rule fixes.
Sometimes, Wizards bundles Theros with other settings in humble bundles. Set an alert on Humble Bundle or Fanatical—they regularly offer $1,000 worth of D&D PDFs for $25.
Wizards of the Coast released a free 15-page PDF called Mythic Odysseys of Theros: Player’s Guide via official channels. It includes: