There are a lot of variables.
I buy my primers by the 1000. So, what are they now a days? Maybe $30 or $.03 each.
Bullets really vary based on caliber, weight, lead, jacketed, supplier, mfg., type.
Powder cost also varies. Most is $20 - $30 a pound. Depends on how much powder you use per shell and the type of powder.
Just so many variables. The only way to compare is to chose one or two calibers and develop a load to compare with.
Years ago, one could save about 50% compared to new shells, even if you bought factory bullets. I reload center-fire rifle shells. I feel like I'm saving some money but I like to be able to vary from what is available on the shelves. For example, I load 30-30s with a 125 gr. flat nosed hollow point, for coyotes and load my 35 Rem. with Hornady 180 gr. XTP for whitetails. I also loaded both with the Hornady FTX Bullets.
I would reload pistol shells like the .357, 44 mag. and 41 mag. However, I would not reload pistol shells like 9 mm or 45 acp. The saving is minimal unless you cast you bullets.
I load my own 12 ga. shot shells. Last time I checked, they cost me $4.85 a box for a quality shell compared to $6+ for the cheap stuff at Walmart.
So, there is at least a 20% savings, maybe more, and you get a quality load that was made by you. And you can customize a load that isn't sold in the stores. I shoot a lot of 1 oz. high speed loads in my 12 ga.
If you want to pick a cartridge or 2 for us to build on, we'll be glad to put something together for you to compare. I'll have to search the web for prices cause I've lost track. Haven't bought anything in the last year or so.
Don't forget, you're looking at a couple hundred buck, or more, for equipment to get started. And if you cast your own bullets, that's another investment plus the hassle of finding a lead supplier.
Hope this helps.
Grey