You'll find that frequency and style of practice ranges from weekly drills for dedicated citizens to yearly basic qualifications for law enforcement officers.
There is no standard.
As time goes on, you'll find that you're confident in your skills and you won't need to burn through as much ammo to practice. You'll be refreshing your skills, not building them.
This doesn't have to be the case for you. Building skill does not mean blazing through ammo. Simple drills consisting of drawing and aiming can help. I'm sure other threads around the board and other replies here will help give you some more feedback that you're looking for.
Some may take my statements as an affront to the philosophy of constant self improvement, but I mean no disrespect. I'm just trying to take an objective look at average practices by average handgun owners. Some assumptions are made, but I hope they're not too far off the mark.