From what I read in R32, the PWM COTS servo would apply here, so you would have to be able to purchase the motor for <$75. The R32 blue box may provide some insight. The RoboRIO is limited to 2.2A on the 6V rail. It may be beneficial to investigate using one of these
Q&A may have some answers as well. All I could find for "servo" was
this.
I also assume you are interested in the 6V RC Control version such as
this. You may want to consider
this (also available
here) if you are not already.