I would recommend you look at John Dobson's _Learn New Testament
Greek_, published by Baker. Dobson takes a helpful step-by-step
approach (e.g., giving the student practice with first person verbs
before introducing second person). The student gets into the New
Testament quite quickly through that course, and that encouages
people to stick with it.
Of course you will generally lose some folk anyway from a volunteer
program once they discover they actually have to work at the
I also suggest you contact Pam Everly at email@example.com.
Pam has taught at least two sessions of church-based Greek courses
and has been developing materials with that goal in mind.