I need to try and remember where I saw that list (2 or 3 products) of alternative pH adjusters in order to post it. But my opinion is most all household products wont provide a stable pH. That is, they will fluctuate quickly after being adjusted. The question is valid (I've asked it myself), and there may be people who can give better advice based on their experiences with using it (I haven't). When I first started growing hydroponically I was always (still do) looking for cheaper alternatives (especially because I often need to have things shipped). But one of the things that I don't feel necessary to find is a cheaper alternative for is pH adjusters.
It would be good to know if a supply got hung up in mid grow (and I had no choice). But other than that I don't see a need. I can get a 1-2 year supply for about $10-$12 (plus shipping). I'm cheep, but I can easily work with that. And now that we have a hydroponic supply store in town, I don't even need to pay for shipping. Keep in mind that just changing pH isn't the only factor involved either. Depending on what's used, the
nutrient availability and/or amount of elements can be affected too (especially if you need to reapply it regularly). Also by adding something to the nutrient solution, you change (raise) the EC/TDS/PPM each time. But that wont mean you have a balanced mix, just that a certain amount of minerals (regardless of what they are) are conducting electricity in your water (that's how all meters read nutrient/mineral level regardless of how they convert/display it). The more you add, the more it will conduct (thus the higher reading you get). But that dosen't mean you have a good nutrient mix. To test that theory, just pour a bunch of baking soda into plain water until you reach the desired reading. Then see if then plants grow.