Best way for us in North America is with the surveys and watch the videos(the rest of the world doesn't get as much opportunity)
It takes some time but they add up
Between them you should get enough to keep you in Balls
I check them out before I play usually - some days I latch onto a couple surveys and it takes about a half hour - but getting 60, 90, or whichever seems worthwhile for myself
Been fortunate over time that I have not had to put any cash out to buy equipment - and in the time I was waiting to earn enough, well I spent that figuring out different aspects of the game (how the wind affects, putt speed etc)
I'll add one other thing from my own experience - in our Country Club a member just made Tour Master and has only ever used starter balls
Or you can buy credits
Good Luck and welcome aboard
Luciano