How much can I save by reloading?

The short answer is, "a lot".   Exactly how much you will save depends on the caliber(s) you will reload.   The table below shows the typical savings that you can realize on some common (and not-so-common) handgun calibers by buying good quality jacketed bullets (except where indicated) and other components in bulk, using your own brass, and loading them yourself.

Caliber Retail/50 Cost to Reload /50 Savings % Savings per 1K rounds
.380 $19 $5.73 70% $265.40
9mm $15 $7.32 51% $153.60
.38 Super $32 $7.06 78% $498.80
.38 Spl (Cast lead) $22 $5.07 77% $338.60
.357 Magnum $28 $9.43 66% $371.40
.40 S&W $21 $8.12 61% $257.60
10mm $35 $8.83 75% $523.40
44 Spl (Cast lead) $40 $6.40 84% $672.00
.44 Magnum $39 $14.10 64% $498.00
.45 ACP $23 $8.75 62% $285.00
.45 Colt (Cast lead) $40 $8.07 80% $638.60
.500 S&W Mag (Cast lead) $100 $33.45 67% $1331.00

The retail prices are for a box of 50 cartridges, and are from my local shop (in Middlesex County, Massachusetts) in September of 2012.   The costs for bullets and primers came from online bulk retailers on the same day (prices include typical shipping and hazmat fees).   I'm using $25 per pound for the cost for powder (this is a little high).   The resulting reloads quoted below will be duplicates of good factory ammo.   (I know it's not an apples-to-apples comparison, because the retail prices are per box, and the component prices are for bulk quantities, but bear with me here, I'm trying to make a point).  

Notice that you'll save the least when reloading ‘commodity' calibers such as 9mm, 40 S&W, and .45 ACP.   With these calibers, most of your cost savings will be due to the fact that you'll be reusing your brass.   Even so, if you shoot a couple of boxes of 9mm per week, you'll more than pay for a basic progressive setup in the first year.

The retail price for less common handgun calibers is much higher because the manufacturers make it in smaller lots, and the demand is lower.   This is where reloading really pays off.   For example, the retail price for .38 Super is more than double the cost of 9mm, however is costs only a cent or so per round more to reload .38 Super than it does to reload 9mm.

The savings is greater still when reloading rifle cartridges.   A couple of years ago, a friend bragged about the great deal he got on a barely used Weatherby rifle in .340 Weatherby Magnum which he planned to use for elk hunting.   The bragging stopped when he found out that the ammo he wanted to use was going to cost $6 per round, and had to be special-ordered.

.340 Weatherby ammo is very expensive
You can save $4.50 per round if you make this ammo yourself

Fortunately for him, his rifle came with a few boxes of once-fired brass.   After a $375 investment in equipment, he was able to buy components and reload ammo identical to factory for $1.50 per round.   His complete setup was ‘paid for' before he fired his 84th round.

..500 S&W can be made for $0.20 per round if you cast your own bullets
Casting your own bullets can save you a small fortune

The savings becomes downright astronomical if you cast your own bullets.   For example, you can cast and reload very high quality gas-checked 500gr S&W .500 flat-points for about $0.20 each, which represents a savings of over $2500/1000 rounds when compared to factory ammo.