It's the principle more than the size of the expenditure:  Several years ago I heard about those units that heat-seal foods in plastic for long-term freezing, but I was reluctant to spring for the purchase price.  Then I saw an ad for a tiny, battery-powered hand-held version for $10 and ordered it.  At first it sort of worked, albeit not well; I had to squeeze really hard, and then it only created a very thin, weak, flimsy seal I could too easily break.  Soon thereafter, the entire thing simply fell apart.  Yes, it cost less than the $50-150 range of the real heat sealers--but it was a waste of $10.

In the same vein, a long time ago I learned the hard way about buying "bargain" brands of some paper products.  When my brother and sister-in-law asked me to pick up some baby wipes for them, I got the kind that cost half as much as the big brand name.  They ungraciously but accurately pointed out that these were so thin you had to use twice as many, negating the apparent savings.  Similarly, when friends asked me to pick up paper plates, I brought back a brand that cost half what Chinet did, and one of these friends--again, correctly if ungratefully--told me they were so flimsy you'd have to use 3-4 together to approximate the sturdiness of one Chinet plate, so they weren't really a bargain.  In both instances, the feedback I got was accurate, so ultimately I'm glad to have learned something about price vs. quality.  Of course, also in both cases, the people who asked ME to do THEM a FAVOR could have avoided being so rude and inconsiderate by either making the effort to go get what they wanted themselves instead of taking advantage of my good nature; OR at least telling me what brands they wanted!  So I not only learned about quality vs. price; I also learned not to offer to do people favors--or at the very least, to make them specify exactly what they want first. 

Generally, I think it's best to examine something in advance as much as possible and try to ascertain its quality, rather than focusing only on the cheapest price.