[WS:] That is not how I interpreted the story. It is all about buying social status - by declaring that she lost the necklace and cannot replace it Mathilde would have lost the status that she craved.
Working to replace the missing bling was the price they were willing to pay to preserve that status. The actual value of the bling was irrelevant.
You can easily apply this logic to the behavior of most people, not just the working class. They buy suburban homes made out of plywood, plasma tvs that become obsolete before they are paid for, gas-guzzling suvs, go to expensive places or, for that matter, buy actual bling and expensive sneakers etc. - go into debt and work their asses off (or steal and go to jail) to make payments. But it seldom occurs to them that they can comfortably live for much less - they point is that these so called "material" goods are not abut material living conditions but about quite immaterial social status. taking a train can take from point A to B just as easily as driving an SUV, but it does not entail the same social status. Most people choose status over utility & material living conditions.