The financial answer is that it pays when you have shot enough to break even $ on the equipment and components used to that point. After that your savings begin.

I could say that I can reload for .07 a round but I would be figuring with primers that cost $10/k power that cost $15 and bullets that cost $10 because I bought a lot back when those were the prices.

Current prices seem to be $30-$40/k primers, $25+ powder and bullets range from $16 to $30 or more so it's hard to start out from scratch and see any real savings for a while

Assuming brass costs you nothing and you buy jacketed or plated bullets...
Rough estimates for pistol are 3.5 cents for a primer, 16 to 20 cents for bullet and 2 cents for powder so .21 to .24 each for .40 or 9mm is an average reload cost that is currently very close to what you can buy a case of range ammo at. Sure you can pare that cost down some to about .16 each but then you have to buy components in bulk or find a deal which means hundreds out at one time.

If you cast your own bullets, even then it isn't free because you have fuel/elec costs for the melting pot, gas to go collect the WW, lube cost and maybe a few other items so they do cost something. Then there is all the time you spend doing it... but time is free unless you are giving up a paying gig to do it.