I keep an inventory in an Excel spreadsheet of everything I have on hand and update it about every other year (bi-annually). I should keep one for everything I have shot, which would complement the first (but that's another Thread). The inventory is quite extensive. Try it yourself. You will be amazed at how much "stuff" you have.
I know what I paid for the 'Fixed Assets' part of my inventory: rifles, pistols, range bag, gun cases, presses, dies, rifle & pistol cases, shell holders, scales, powder tricklers, etc.
I know what I paid for the consumable part: powders, bullets, primers, etc. I estimate or count how many consumable parts there are on hand. Estimates are faster.
The updated inventory 'TOTAL' is a loose measure of my investment (SUNK COST). It is easy (using Midway, Mid-South, Gun Brokers.com, and on-line resources) to extract TODAY'S unit prices for most of the pieces in the inventory (some pieces are "extinct" and no longer made) to get the DELTA between TODAY's cost versus what I paid for the same inventory. Tells me an interesting story.
It is easy to determine how many reloaded rounds of a single caliber are necessary to EQUAL the AVERAGE COST of Factory ammo for that caliber while OWNING the equipment that built the rounds. Ask me about it and I will describe the method further.