Just because you receive blessings, even an abundance of blessings, does not mean you have not made a sacrifice.

President Oaks had a talk titled Sacrifice, discusses the sacrifice missionaries make extensively
Elder Hales had a talk titled Couple Missionaries: Blessings from Sacrifice and Service

Other talks:
One More Day By Elder Taylor G. Godoy, "We all have a “today” to live, and the key to making our day successful is to be willing to sacrifice."
Certain Women By Linda K. Burton listed under the Topic of Sacrifice discusses the sacrifice of time, service, effort... of missionaries and The Joy of Unselfish Service By Cristina B. Francohers also listed under the Topic of Sacrifice discusses similar subjects