I have since bought more than a dozen glasses from zennithoptical.com, at a total cost of about $300. And by using the technique, the prescription on both of my eyes dropped by 1 (from -5.75 to -4.75). Unfortunately that seems to be the limit of that technique. But I was extremely happy to find a source for cheap yet good glasses. Now I have two normal prescription pairs for daily use like driving, two more pairs for reading (1 for backup for each).
So the cheapest way to get glasses now is to get a prescription at Costco (cost about $40), then just buy your glasses online.