No cheap ammo here but if I did it would probably be Speer Lawman which has similar characteristics and dimensions to Gold Dot.
I personally agree with Tracker. Lawman can be purchased at a fair price and runs great in my R9. As he has stated it is designed to be a range ammo that mimmicks the performance of Gold Dot.
All of that being said I have been advised to simply shoot what I carry. Though I don't do this every time I am inclined to and try to do this most every time. Once your gun has been proven to be reliable then I would pass along the info that was given to me. Just shoot what you carry and keep that to a minimum.
In other words just every so often fire off the mag and spare mag you have been carrying and clean it and repocket it. This is an in close gun that you probably won't have to shoot like you are 007 (or at least we hope not) if called upon to do so in a defensive situation. That being the case extensive range time is not recomended or necessary.
Best of luck with your R9. My favorite pocket 9.