Money talks and bluster walks, so here's the facts.
Using LuckyGunner.com's price data for PMC 9mm & .45 Auto FMJ Ammo,assuming $55 for constant per-month range incidental costs and setting a 1000 rounds per month training goal, we observe a $2,400 difference in annual ammo cost between 9mm and .45 Auto. That can buy a lot of Klondike Bars folks.
The next chart compares what the year end total counts would be , assuming a shooter has a $100.00 per month ammo budget and shoots that from January to December. The mixed chart assumes one shoots 9mm six months out of the year, and then .45 for another six months.
Whether the expense is worth the benefits is a decision each shooter has to make for themselves. But there's no mistaking the data- .45 Auto invokes a decisive resource cost compared to 9mm.
The next topic : applying training costs plus retail price to compute a "Total Firearm Cost" metric.