Um, startup costs. You can get going almost dirt-cheap, the thing is...eventually you wind up craving and then getting the really good stuff (Dillon RL550b etc, with all the accessories, that's not cheap, but it's worth it to many).
So... the real question is more like cheapest initially, or cheapest long run? If you're going to wind up with the good stuff anyway, it's cheaper to skip the intervening steps, even if that's not strictly speaking cheap right off. You certainly don't have to go overboard even then as I did - I have every single manufacturers dies for .223, all of 'em, as when I was competing, I felt like leaving no stone unturned (and 5 or so presses). You don't have to get that crazy and buy every tool and gimmick out there though.
That said, I find the Lee dies better than almost anything else in a non progressive press, and Lee makes cheap presses and a cheap powder measure that is actually just as good as a better looking precision-built one I bought for benchrest shooting for a few hundred bucks. If anything the Lee powder measure is actually more accurate!
So, if you're willing to go non progressive, there's a lot of cheap but decent stuff out there; I use midwayusa.com for most of this kind of thing - they are a zero bullshit outfit - though Dillon would have to win that prize as the very best to deal with overall - everything they sell is lifetime guarantee, period, no questions asked.
I'd probably go with some good fixed press - RCBS at the top end, Lee for cheap if you want to be cheap. Then get good dies. For .223 reloading for AR's, most people full length resize, so you want a fairly heavy press with a long handle for that. The other ops can be done with the cheapest crap imaginable - the accuracy is in the dies and the setup, not the press itself.
Dillon .223 dies are the best out there for .223 if you're full length sizing, their case lube is awesome too. If you're reloading to shoot in the very same gun, always, the Lee collet neck sizer die is the real shit - and no one else makes one. That's what I use when I'm out to set or break a record. It makes by-god the most straight and accurate ammo there is, but eventually neck-only sizing will give you miss-feeds or jams as the cases start to fit too tight in the gun.
I use a vibratory tumbler to clean the brass, and use lizard litter from the pet store for the media with some case cleaner (basically toothpaste, mild abrasive). The lizard litter is crushed walnut shells at a fraction of the price they get from a gun supplies place. Everybody sells cleaners, just find one on sale, they're all about the same. The dillon strainer that lets you pour the brass and junk into a thing that spins over a bucket to get all the media out of the brass is the tits - but you can also use a kitchen colander.
OK, here's some links and numbers. The price on the Dillon dies HAS gone high, but they are a lifetime thing, solid carbide.
http://www.dillonprecision.com/#/co...bide_Rifle_Dies__Individual___Three_Die_Sets_
But the Lee stuff is still inexpensive, here's a pretty complete kit for ~$118
http://www.midwayusa.com/product/121744/lee-challenger-breech-lock-single-stage-press-kit
You still need a way to put in primers. The die for the press is pretty good, I use a handheld tool when not using the dillon, but I've heard Lee's is one to avoid. RCBS might be better there. I use a high priced one from Sinclair, and you'd not believe what's essentially a special pair of pliers can be worth over $100, till you use one.
It's like good sex in the way you can feel the primer go in, oooohhh. No kidding, when you're out for that last bit of accuracy, the good tools rule. If you just want reliable, almost anything works
if used right (and you do the QA scrupulously either way).
Then of course, you need dies, and the powder, bullets, primers. I buy primers in 1000 lots, powder in either 1 or 8 lb lots, and bullets in 100's for testing but 500's for real use. I often get the goes-bang hasmats at a local gun show, as the shipping fees are pretty stiff for a small purchase.
I of course have opinions about what works best in AR's, since I have a few, so if you want recipes, let me know.
Inexpensive dies:
http://www.midwayusa.com/product/434975/lee-pacesetter-3-die-set-223-remington
These will wear out in "only" a few 10 thousands rounds...the Dillons will last forever.
I have about 50k rounds through mine (several worn out barrels worth) - they're still new.
I usually get brass wherever I can find it, often as not, winchester or lake city can be found cheap on sale (best for the money, and with "extreme prep", the best period).
Most of the "fancier" pricier brass just isn't worth it either way. Most of it is too soft an alloy for an AR.
Sometimes the milsurp has "crimped" primer pockets that make it a little harder to tease a new primer into them. It's not as big a deal as some make out if you have a little sensitivity in your fingers when you seat them. A primer pocket reamer from Lee or Lyman else can cut that crimp out, but by the second-third loading it's gone anyway.
Then if you really want to "save" money, you get tools like brass trimmers etc so you can get more uses out of the same brass. You at least need to measure it after sizing to make sure it hasn't stretched to the point of causing troubles (brass flows from firing and resizing, it gets longer to the point it won't chamber, or pinches the bullet in the chamber, not good).
Any good reloading manual. Sierra's loads are on the hot side (best bullets, though), and Lee's are on the low side, reflecting their various philosophies. Lyman is a good middle ground. I have all those and some more. Those all go into great detail about the processes, and why each step is important. The cheap compilation handbooks are interesting but lack that teaching feature.
Guess I should make some private youtube video of this process, it's pretty easy once you've seen it done, but can be confusing to just read about. Then it's easy to decide what tools you think are going to be worth buying.
Looks like if you go with the Lee stuff, an inexpensive tumbler, at least one good reloading manual (Lee/Lyman/Sierra) and a couple accessories (like the quick change holders for the lee press, or a good digital scale) you'll have money left over from 6 bills, handily. You should still have some left after getting some components...