Hi Kleinman-Green,
You can read about some of the pros and cons of different types of mattress protectors in post #89 here.
Generally differences in prices will have to do with the different costs of materials such as more costly foam types or more costly covers or quilting either in terms of actual manufacturing cost or the price paid by a particular manufacturer (which also depends on the volume of their purchases and their sources), the amount of more costly materials (3" of a certain material vs 2" for example), differences in margins and the relative costs involved in running the business, and on how many layers of profit margins there are in between the original manufacturer of the raw materials and the purchase of the finished mattress.
Specific mattresses may also have different margins depending on their budget range (in general higher cost mattresses will usually but not always have higher margins) and there are also other factors built into mattress prices as well such as the estimated cost of any return or exchange policy, the cost of shipping (either initially or for an exchange), or any other extras that are provided with the mattress all of which can either be included in the cost of the mattress or added as extra costs.
Phoenix