Answer to first question; in 12 gauge you're not going to save much, if at all. 12 is the most common gauge and shells can be bought for roughly 10% over the reloading cost.
When you factor the cost of components (primers @ 35.00 per thousand, shot at 45.00 per 25# and then wads @ 8.00 per bag of 250) and lets not forget the loader itself (250.00 to 400.00) the savings just aren't there.
I'll disagree - my reloads cost me $3.50 per box, the cheapest store bought stuff runs $6.50 OTD - that's $3/per box difference and I'll shoot over 500 boxes in a year, so that just bought me a new Beretta gas gun. Buying components in bulk is how you save money - you buy primers by the 5,000, wads by the 5,000, powder in 8# jugs and shot by the hundredweight, or even better, by the ton. Reclaimed shot brings the cost down further, and loading light reloads for practice makes it cheaper still. Reloading 3/4 oz 12 and 20 gauge loads for target practice gives me 533 rounds per 25# of shot as compare to 400 for 1oz reloads - that's an extra 5 boxes per bag