In general the worst place to buy ammo is retail stores. It's about always a bit more expensive, well, expect for the exceptions to that, which are out there. Buy bulk and save money.
Fact is it's a wrong way to approach things though. If you want to shoot .45 then you get it for the guns that work it and because you like the round. A poor reason to get a different gun is because it's cheaper to shoot. 9mm has for decades been cheaper than 45 acp, 38 Super or 40 S&W, 357 Sig, etc. That hasn't changed.
What has changed is the extra cash folks have to spare. More people reload these days because of that.
You get 9mm because you like the round and you like the guns that shoot it. You get a gun in any caliber for the same reasons. I have single action revolvers in 45 Colt and 44 Special. Not because they are cheap to shoot but because I want them even if I shoot them less than other guns.
If you want to learn to shoot a 1911 in 45 acp then you plan for that and do so accordingly.
If you start with what's the cheapest commercial ammo around as your target for what you want to shoot...well, unless circumstances force you to do so, there are other ways to go.
If you are new to guns and you have one and want a second and you make $10. and hour than the cost of ammo to work with is a large concern and 9mm in a well made semi is the way to go. Down the road, as you earn more money other considerations come up.
tipoc