The cheapest and most effective way is to go organic. I'm not expert and I've never done subcools super soil recipe yet but I'm gonna give it a try when mine's ready. Only difference between mine and the recipe is that he uses new soil and I just re-use old soil and put amendments in it that way. Saved me TONS of money. I think I spent about $100 total for enough amendments to make 2 batches of soil for a total of about 80 gallons of soil. My local hydro store sells FFOF/HF for $15 a bag so 7 bags for $100 with the discount which comes out to around 3 more cubic ft which is like getting 2 bags of OF for free. And not only that, you only need to apply water to the soil and you're set! No need for fancy bottles or any of that expensive unnecessary BS.
And if you're looking for a little extra boost while using that soil, DO NOT use nutes!
https://www.rollitup.org/organics/510995-organic-feeding-101-a-2.html
That guy at the bottom page as well as the OP's first post have some amazing recipes. The best part about them is you likely have a lot of the ingredients already since you made super soil, so a lot of the stuff can not only be made for free, but it's typically more powerful than the stuff you're paying $20+ per small bottle. AND, the posts say that you only need to apply every one or two weeks. Definitely look into that