The main challenge with cheap jewelry is a general lack of quality and, therefore, longevity. Producing high quality jewelry is expensive, both in labor and materials. Sure you can set a ring with CZ instead of a diamond or multiple diamonds, but CZ will darken over time and, in some cases, will even become completely black. You can also go with cheap metals, such as zinc and copper, instead of, say, white gold or platinum, but those often leave your skin grey/black and also tarnish over time.
Ultimately this doesn't make cheap jewelry right or wrong. Just like people who purchase IF diamonds are not better or worse than those who purchase eye clean SI1 or VS2 diamonds. One is eye clean and the other is "mind clean". Ultimately it all just depends on what is important to the buyer.