For carry ammo (.40 S&W), I spare no expense. I couldn't tell you how much it cost me. I bought a bunch of good stuff years ago and still have enough for my mags.
For target ammo, I try to use the cheapest I can find. Right now, that's Blazer Brass from Walmart in a 50 round box. The box cost me 12.97 / 50 rounds...so about 26 cents per round. I used to buy Winchester White Box (WWB) by the 100 round boxes. That was when the price was $16 for 100 rounds. Now the WWB costs me 28.97 per 100 rounds. So around .29 / round. Economically the BB is cheaper. I have not had any malfunctions with either BB or WWB in my G23.
Note. I am shooting alot more 9mm and .22 these days than .40. I was hoping that ammo prices would start to drop with the gass, but no luck so far.