Train as often as you can, and for as long as you can afford. You don't necessarily have to shoot live ammo to train though. As I type, I'm on the middle of dry-firing. I have a t-shirt on a hanger hung on the wall across from me. I pull the trigger, pull back the slide, then slowly let out till reset, then pull again. Do that for 30 minutes before bed everyday for a week, your double tap groups will probably tighten up. Also helps smoothen out the trigger. When I go shooting, I typically shoot 50-100 rounds. I go whenever I feel the urge and I have a spare hour or two. My range only charges $5, indoor or outdoor. Or I go to the woods and shoot my steel plate for free.
When you train, (if the range allows, another +1 for the woods) practice drawing from concealed, double taps, and while moving.
Realistically, if you can hit the range once a week and shoot a box or two, that's pretty good. If you keep that up, you'll shoot anywhere from 2600-5200 rounds a year. If that's factory 9mm, that'll run you about $500-1200!
Shooting is so dang expensive..........that's why I started reloading years ago. When I started casting, my prices dropped even more. I can make a box of .357 for under $4