There is a theory that the same ammo should be used for practice as for carry, the idea being that the recoil, accuracy at various ranges, and even the sound vary.  This gets technical pretty fast.   For example, supersonic vs subsonic ammo clearly is different - both in accuracy, sound, recoil, ability to fire successive rounds, ability to aim.

HOWEVER - It's likely that anyone with a grain of sense would limit practices with $2-4/round ammo (eg high grade hollowpoint) to a very few very specialized operatives.  Think in terms of seal teams, CIA agents, stuff like that.  If in fact that's routine it would be extremely, extremely wasteful of taxpayer funds.

The primary way to get better training would be to simply train more often.  For example, most police train once a year.  One box of 50 shells.  Should be the cheapest that's reasonable similar in ballistics to the carry ammo.