Differences are in the jets, jet design, filtration system, insulation, hardiness of the shell. You will find that the less expensive brands just put in a gazillion jets to try to impress the consumer or very few jets to save $. The better brands strategically put the jets in to act as a sort of accupressure. It is well worth the $ to buy a good one such as Sundance or Hot springs you will be much happier in the long run.
Elise