If you don't want to spend much money, you might be able to buy "Miller Home Draft" and use that instead. The 6L bottles are EXACTLY the same. You can also use 3L bottles from the grocery store (although they're clear, which is bad). One TAD bottle cost $8 (pure and simple rip-off)! How can I say that? Because the MillerCoors unit, including 6L of beer in one of the 6L bottles, PLUS a tap (very similar to TAD), PLUS a CO2 cartridge (16 grams, which is twice as big as the TAD) costs $15 from a local distributor.
So here's a few videos I posted a short while back on the topic. The first one was just the TAD bottle, and the second one was after I ran through my first 6L of beer.
http://www.youtube.com/watch?v=DNHqr-zQ_IE
http://www.youtube.com/watch?v=rLRyYA2khCw
One thing I'll say is that if you want to avoid bottling, you sorta need 3 of the 6L bottles (to hold your 5 gallon batch).
The other thing I learned (if you don't watch the second video) is that you actually can force carbonate with TAD. Not sure if it's possible with the MHD yet, but it's real easy with TAD if you don't mind blowing through some CO2.
Looking at prices for CO2, I found this redrockminnesota.com site that has some good prices. For quantity of 100 8 gram units: $0.45 each, delivered. For quantity of 60 16 gram units: $1.15 each, delivered.
The bottom line for Tap-A-Draft is if you buy at the $0.45 price, you can probably force carbonate your beer at a price of about $6 per 5 gallon batch (use 4 or 5 of the 8 gram cartridges per 6L in the Tap-A-Draft). If you bottle condition, then just use CO2 for dispensing, you could get-by much cheaper (about $3 per batch), only using 2 of the 8 gram cartridges per 6L. Re-using the Home Draft units, the price for carbonation would be similar, although like I said I'm not sure how to force carbonate with the Home Draft units.
--Dale--