 The cheapest way to get our B12 is probably one 2,500 micrograms sublingual, chewable, or liquid supplement of cyanocobalamin once a week. This stuff is dirt cheap. You can find a 20-year supply online for 40 bucks. All the B12 our body needs for $2 a year. Of course, this stuff doesn't last 20 years. There's a four-year expiration date, so share it with some friends. For those mathematically minded who are thinking, wait a second. If you only need 4 to 7 micrograms a day, why do you have to take 2,500 a week? Well, it's a little complicated, but let's do it. Our B12 receptors become saturated at as little as 1.5. So we can only absorb 1.5 at a time through our receptor system. But about 1% of the rest passively diffuses right through our gut into our bloodstream. So for those of you into this kind of thing, let's do the math. When we take a 2,500 microgram dose, we absorb 1.5 through our receptor system, and then 1% of the 2,498.5 that's left. So inside our body we now have 1.5, plus that 1% comes out to be about 26.5. You do that once a week, and that averages to about 4 micrograms a day. So we should take at least 2,500 micrograms once a week. We could take 3,000 a week, 5,000. If you take too much, all you get is expensive P, and at a couple bucks a year, it's not even that expensive. Even though it is a water-soluble vitamin, we don't have to take it every day because throughout our evolution our bodies were so used to getting such tiny amounts, you know, maybe some woolly mammoth pooped-up stream or something, that our body devised an ingenious way to hold on to it. So that's why we can do this kind of averaging over time.