You know the $20 shoes won't be great, and sure, it's possible the $200 shoes will be better than the $20 ones...or they could be exactly the same.
It mostly came down to examining the stiches and seams for quality, which is what I always do now when buying clothes. Look for unraveling, loose or missed stitches, not-straight stitching, etc. Pull the seam apart lightly and see how it holds up.
Also things like zipper quality (YKK is a top brand, and would be stamped on the underside), or how well stripes are lined up. Do the button holes look well stitched?
Take boots, for example. He earned thirty-eight dollars a month plus allowances. A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. Those were the kind of boots Vimes always bought, and wore until the soles were so thin that he could tell where he was in Ankh-Morpork on a foggy night by the feel of the cobbles.
But the thing was that good boots lasted for years and years. A man who could afford fifty dollars had a pair of boots that'd still be keeping his feet dry in ten years' time, while the poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet.
This was the Captain Samuel Vimes 'Boots' theory of socioeconomic unfairness."
The way I see it, frugality should be "I don't need 10 pair of sneakers, I can probably do 2 quality ones, and take care of them so that they last" and not "Let's buy a couple of those cheap $10 sneakers from HnM". Spend where it matters, but don't spend because you can or because you want something impulsively.