Microsoft Certification Booster Packs are sold for $200-$225 depending on the package and your country. This basically means that:
For $200 you can choose between “1 Exam + 30 days access to online practice test” or “1 exam and up to 4 free retakes of that same exam”
For $225 you get “1 exam and up to 4 free retakes of that same exam AND 30 days access to online practice test”.
It seemed like the Microsoft Certification Booster Packs promotion would end 31-08-2016, but they extended it to 30-09-2016, making this week the last week you’ll be able to purchase it.
After purchase, you’ll have 6 months to use your booster pack(s).
For more information, see my previous blogpost https://blog.bjornhouben.com/2016/04/19/certification-my-thoughts-on-microsoft-certification-booster-packs/ or the Microsoft website https://www.microsoft.com/en-us/learning/offers.aspx