I don't know of homebrewer that amortizes their equipment cost into the cost of their beer. It's ingredients only. For kegging, the equipment is another expenditure much like brew kettles and such, but once you have it, it's cheaper.
Is it? Bottles are free. Caps cost at most $1 per batch, and priming sugar costs maybe $0.50 per batch. That's $1.50/batch. Factor in an additional 50 cents for the extra effort, and that's $2/batch. Capper and bottling wand cost maybe $25 total.
Assuming you got lucky and spent $30 on tank, regulator, and faucet. $50 on a mini fridge (though personally I'd be buying bigger fridge). Then let's say $50 on ONE keg, you're up to $130. Minus $25, that's $115. It'd take more than 55 batches to recoup the cost, and that's ignoring the cost of running an extra fridge (assuming you are putting a few bottles in your regular fridge at a time).
If we assume $40/year to run the extra fridge, that's another 20 batches per year. For me, my costs wouldn't get recouped based on that. Heck, even if the fridge only cost $20/year to run, I'd only barely recoup THAT cost, and that's assuming I don't decide to do any bottling from the keg.
If someone is going out and buying new kegging equipment for the major components, they're missing the point. Plenty of used equipment around for great prices.
Not so much from what I can find. I can find plenty of cheap fridges, but cheap kegs and CO2 equipment are hard to come by, and I live in a big city. I think there was only one CO2/keg set up I could find that I thought was a good deal, but that would have meant driving all the way to Delaware.
Granted, I can find some cheaper small keg fridges that use single tap towers, but that's not what I personally want. I want a larger fridge so I can put three taps on, and use it for other purposes.