Doesn't matter if the AS is readily available or not, does it? Low tech is still low tech. I think there should be some more specifics about what this $50 discretion can and can't include. Rather, I think the entirety what we can suggest for him to use would be more adequate...
Why can't AS be low tech?
It's a hobby fallacy that "low tech" has to = Walstad NPT with dirt and ugly plants. If he really wanted to go low tech, he could just use inert. That's even cheaper and comes without a lot of the hassles of potting soil. Have you ever tried to look for potting soil for aquaria? I have, it's even MORE of a hassle to find than just ordering some AS and being done with it. That's not even getting into the ridiculous process of mineralized soil. Really, you only start seeing benefits with potting soil when you start getting into triple digits gallon wise.
Part of the point of "the method" is to get it right the first time. How many successful and attractive nano tanks have you seen long term with potting soil? I've seen about none. How many tanks of varying "tech" level have you seen using AS? A whole lot.
What comes down to it, is it's his challenge, so if he wants 50$ to cover his bases against, well, having to use potting soil, those are his terms. I have no doubt that if TPT really had their way, it would end with forcing him to de-rim a 2.5 in a cave with a box of scraps.