http://www.handloads.com/calc/loadingCosts.asp
or just do an internet search on the phrase "Cost of reloading" or "reloading cost" or phrases like that and you will find dozens of cost calculators. There is even one that has a downloadable EXCEL spreadsheet you can use offline.
Gamestalker hit the nail on the head mentioning the OTHER advantages of loading your own ammunition.
Let me count the ways:
Economy: Depending on what cartridges you are reloading (and whether or not you want to count your time and the up-front equipment costs) you can save anywhere from just a little to 80% or more of your ammo costs. (9mm is very close to no savings. 500 S&W, my friend's ammo costs are $0.75 per round, factory loaded ammo is $3.00 each for comparable ammo. More exotic calibers (especially rifle calibers) can save even more. Some rounds are not even available on a regular basis at any price.
Quality: Ammo you craft yourself can be tuned to your firearms particular characteristics. Handloaders for rifles quite often find some individual guns have quite striking differences in group size when shooting tuned ammunition.
Knowledge: As you study reloading, you will, perforce, also study internal ballistics. The study of internal ballistics leads into the study of how your firearm works.
Customization: Ammo you load yourself can be tuned to your particular needs. My friend with the 500 S&W loads full power loads and "powder puff" loads that clock 350 grain slugs a little under 800 feet per second. I know that's more than a G.I. 45 ACP's power and momentum, but they shoot like 22 rimfire in that big, heavy gun. Great for fun, familiarization, training and letting the curious bystander go for a "test drive" with a super-light load, a medium load, a heavy load and, if they are still game one of the big boomers. This tends to avoid the "rear sight in the forehead" mark.
Satisfaction: Punching small bunches of small, medium or large holes in paper or bringing down a game or food animal with ammunition you crafted yourself has a good deal of satisfaction. Same reason I prefer to make my own biscuits instead of store-bought.
Smug satisfaction: When the ammo shelves are bare during a market or political scare, loaders are demonstrably less affected by the shortages. A couple of pounds of powder, a thousand primers and bullets (or few pounds of lead) and a hundred cartridge cases wouldn't fill a small book carton, but lets the loader know he can shoot while price-gougers take advantage of non-loaders.
Self-satisfaction: The repetitive, calm, attentive concentration of the reloading activities is often found to be so much fun as to bring to the shooter's mind the question, "Do I reload so I can shoot shoot or do I shoot so I can reload?". Some find loading to be as satisfying a hobby as shooting or fly-tying or many other hobbies.
The more fanatical among us combine a couple of the features I have mentioned and, instead of shooting for bullseye accuracy at the range, reload in a search for the "magic load" that achieves perfection in a given rifle. Then, they move on to the next target, which is another rifle and another tuned load. But you do have to be at least a little fanatical to even get it. It is the hunt they seek, for they enjoy the quest more than the goal.
I am sure there are many other reasons, but these are the main ones I can think of.
Handloading is not rocket science, but it does involve flame and smoke and things that go very fast, so caution is appropriate. If you can change a tire without losing your lug nuts and follow a cake recipe reasonably well, you can reload.
Thanks for asking our advice
Lost Sheep
Good Luck.