Real black powder is still routinely available from mail order outfitters. The issue isn't availability so much as cost - mail order involves paying a $22 hazardous material shipping fee, which most people are reluctant to do.
That Haz-Mat fee also applies to any of the fake powders. So now, lets compare apples to apples.
A case of 25 cans of GOEX from Grafs would cost me $15.97 per pound to my door. I don't know why, but Grafs website automatically charges a double haz-mat fee ($45) for an order over 20 lbs. of black powder. As far as I know, the haz-mat fee is supposed to be $22.50 for any package up to 70 lbs. gross weight (which would cover up to 2 25-lb. cases of GOEX) Assuming that the haz-mat fee calculation on Grafs website is incorrect and the normal $22.50 fee would apply for a case of 25 lbs., it would only be $15.07 per pound to my door.
Before I order my next case of GOEX I will call Grafs and ask about the Haz-Mat fee, as it doesn't increase beyond $22.50 per case of 25 lbs. for any of the fake powders I checked. But for 2 cases (50 lbs.) of GOEX, it jumps to a triple fee of $67.50. If this is correct, I may have to take my powder business elsewhere, as it seems Grafs is over-charging on the Haz-Mat fee.
A case of 25 pounds of Pyrodex from Grafs would cost me $15.67 per pound to my door. Cabelas sells Pyrodex RS for $19 per pound.
A case of 25 lbs. of Triple Se7en from Grafs is $22.07 to my door. Again, Cabelas sells Triple Se7en for $27 per pound.
While Grafs is pretty cheap for the fake powders, they are one of the more expensive vendors for GOEX. I could certainly do better by shopping around, but I wanted to compare apples to apples. For example, according to their website, I can get a case of GOEX from Jack's Powder Keg for $12.60 per pound shipped.
By the way, Dixon's charges $20 per lb. for GOEX. I don't know about any of the fake powders that Dixon's might sell, as I have no use for any of them. A little steep, but sometimes you have to pay a little bit more for convenience. I just bought a pound of FFFg from Dixon's las week as I have been out of work on disability for more than 4 months and can't afford to order a case until I start getting a paycheck again.
So when you compare apples to apples, black powder is no more expensive than any of the fakes, and is in fact cheaper than many of the fake powders.
As far as splitting a case among a couple of shooters - why bother? I shoot a MINIMUM of 10 lbs. of GOEX per year. So a case lasts me about 2 years. And as long as I plan ahead a little bit, I never run out of powder.