This 'issue' comes up a lot in training. Fly with ten different instructors and you will get ten different ways of doing things, and ten different "personalities" and abilities from the instructors.
Yes, a decent auto is hard to teach to people, esp when you are a new-ish instructor (who has suffered an overspeed in the past and needs to keep his job). But, also some students just have a real problem with them and some of them blame the instructor. Some students think they are better than they really are, some instructors aren't that good at teaching either!
I would have a quiet word with your instructor, tell him you feel you would benefit from doing a few flights with a different instructor, no hard feelings, nothing personal, your confidence is gone a bit, you're worried about money etc. Yes, he might be a little 'upset' but he should understand that teaching/instructing is all about personalities and the student should feel comortable with his instructor. Just be friendly and tactful and it should be ok.
On the subject of R22 RPM in autos, the key is to keep the 60 kt attitude. The R22 RPM is very sensitive to attitude changes, keep your eyes OUTSIDE, do not stare at the airspeed dial. Set the attitude and hold it, then control the RPM with the lever. Start the flare when the RPM is at the bottom of the green arc, as you know it will rise in the flare.
My advice (I'm sure others have different techniques) ... If you are having trouble with RPM control, go up to 3000+ feet, enter an auto and just play around with the RPM, see what effect cyclic inputs/attitude has on autos, do some turns, get comfortable holding the 60kt attitude and managing the RPM etc. It's a lot easier than trying to learn this while heading for the ground at 500 feet.
Good luck.