Determine the price of was missing package

Calculate the price for Was Missing package.

• packageIndex
  • 0 is the Free package
  • 1 is the Basic package
  • 2 is the Advanced package
  • 3 is the Extreme package
• users The count of users/coupons the buyer is buying for
• months Buying for how many months

• The Price the user should see ( and pay )