The game frequently drops to 60-70% off during Summer, Winter, or Driving Simulation sales. You can get the full Home Edition for less than the price of a pizza.
Sometimes the activation window fails to save the key because it lacks permissions. Right-click the game icon and select "Run as Administrator." Version 1.5 Features and System Requirements
: Once you exchange your serial number for a Steam key, the original serial number will be permanently blocked and the standalone version will no longer work. Where to Buy a New Key