when you are in Moscow, a visit to the ballet of Kremlin palace is a must. Usually you can choose from a wide range of different ballets and concerts, which can be bought directly on the website of Kremlin Palace (kremlinpalace.org).
The theatre is located inside Kremlin, so you are allowed to enter the territory only with a valid ticket ( also possible if you want to visit the museum).
The ticket prices are very affordable and for 1000 RUR you can get already a nice seat.
But keep in mind that ordering on the Russian version of the website will offer you a wider range of tickets and also cheaper fares, so in worst case use google translator or simply contact me and I will help you!