All of the BP substitutes work, kinda sorta, more or less. The thing I keep hearing is "I can't get blackpowder around here". That just ain't so, you can get blackpowder anywhere in the U.S. You just have to order it. The $25.00 HazMat fee does add to the shipping cost but if you order at least 5 pounds the cost per pound works out to about the same as Pyrodex at your retail store and a lot cheaper than some of the subs or any of the pellets.
I just checked Graf's online site. Their retail price (glad I don't pay retail) for comparison to your gun store prices, is $13.99 per pound for Graf's brand which is at least as good as Goex, maybe better.
Five pounds with HazMat fee works out to $18.99 per pound.
Ten pounds with HazMat is $16.49 per pound and 25 pounds is $14.99 per pound
You can mix your order, say one pound of 3f, one pound of 4f, and three pounds of 2f, whatevery you like.
There may be better prices out there, Graf's was just the first place I looked. How long will it take you to burn up 5, 10 or 25 pounds? Not as long as you may imagine if you are at all serious about your shooting. I can burn 25 pounds of black nearly as quick one pound of Bullseye, thinking 3 grains of Bullseye vs 50-100 grains of black per shot.