The Monkey Temple is the mos cost effective tower in the game. If you want to get far in Freeplay, it is vital that you have some Max Temples.
For the Monkey Temple, what towers you sacrifice determine its power. In order to get maximum Temple Power, you'll need to Spend:
$30,000 of Bomb or Mortar towers for missiles
$10,00 of Ice Towers for Ice
$10,00 of Glue Towers for Glue
$10,00 of Apprentices for Tornadoes
All of these will be shot out of the Plasma the Temple shoots. In addition, if you spend $30,000 in other towers, it will shoot out 16 Blades like a Tack Shooter.
An easy way to get a max temple is to sacrifice-
Three 4/2 Mortars
One 4/0 Ice tower
One 4/0 Glue tower
One 0/4 Apprentice
One 0/4 Super Monkey
Also, I recommend not upgrading the range of the Temple until yo have given the sacrifices, so you can avoid accidental sacrifices.