well, not to look at differences in quality, for the general layman, theres target ammo and self defence ammo
target ammo is:
usually "ball" ammo, aka, full metal jacket FMJ
also, a lot of times you can find even cheaper steel cased ammo compared to brass cased ammo. steel cased ammo cannot be reloaded, and some people feel they feel and extract less reliably than brass
bullets have a weight in grains to them
self defense ammo is:
usually hollow point ammo, aka jacketed hollow point (JHP)
They can be brass cased, but the ones i have are shiny stainless steel
target ammo for 9mm, as an example, can run you from 9.50 to 12.00 to 16 to beyond for a box of 50
self defence ammo, usually costs $1 a round, usually sold in boxes of 20 or 25.
so self defence ammo can run you as much as 4 times the amount target loads can do.
as for the "you get what you pay for"
variances in powder load, burn consistency, bullet weight, etc
can affect velocity and bullet flight path which in the end affects accuracy
for the layman shooting at 7 yards, this is negligible, but for the target shooter shooting a pistol at 25 yards and beyond, this is a factor