Meh, I don't care how old this thread is. I've got what feels like a good nug to add...
I just did some searching surrounding this, and what Wolvie is saying seems to be fairly close to confirmed.
I've been told not to provide links so search "systemic acquired resistance salicylic acid" if you want more info, but basically when this response occurs naturally at an infection or damage site:
"The most likely trigger for this response is methylsalicyclic acidproduced in large quantities around the infection site. The phloem carries it to the rest of the plant. At sites away from the infection, it is converted to salicylic acid."
...and salicylic acid itself...
"A white crystalline organic acid, 2-hydroxybenzoic acid, C6H4(OH)(COOH), used in the production of aspirin and other industrial chemicals."
So, we're trying to get the end response without the damaging stimulus or even initial damage-response compound, just that which induces the protective, and in our case heady, response for which we're looking. Also, "used in the production of" may not mean "contains" such that you could make anything as effective as Bud Factor X, but I do recall my father having a planter's wart when I was a kid and having to put this weird stuff on it - salicylic acid. Unfortunately, I have a hazy (I think I was like 7) recollection that it had been a prescription...
...actually, just checked - nope, no prescription. "Dr. Scholl's Clear Away Plantar, Salicylic Acid Wart Remover for Feet". So I assume you could find it in a soluble form, then it's just a question of a run through peripheral ingredients for potential problems like "mmm, let's throw some antibiotics in there", some calculations and a little careful testing to reach the right dilution, and you've got home made Bud Factor X...er, well, at least one ingredient that probably exists in it.
About $100 for a litre of BFX.
About $10 for .3oz of concentrated salicylic acid wart remover.
So, if by some luck BFX is really just a dialed-in concentration in solution of SA, I guess it's a question of ratio for value - for the same money, you get about 3oz SA concentrate or 1litre(about 34 fluid oz) of solution. Meaning, if the dialed-in dilution of SA found in these wart-intended concentrates would be greater than something like 11.5:1 water:SAConcentrate in favor of water, then you've matched the BFX price point. Thinking back to seeing my dad put that weird stuff on his plantar's wart (it friggin' SMOKED, I kid you not!), I wouldn't be surprised to find that the ratio is EXTREMELY high, and that the cost analysis works out.
...oooor I could just buy some damn BFX...I do love knowing about this stuff, but the older I get, the more I understand the true and significant VALUE of convenience.
+ edit: continuing to look around about this, and would now suggest searching "Inducing Systemic Acquired Resistance: Helping Plants Help Themselves". So, I guess there are other likely inducements in BFX, but we still may be able to DIY 'em. Looking more and more like the nuances of the best ratios in multiple compounds might bear out the cost of the BFX though...