A cheap buy can be an expensive buy.
You can purchase a trampoline with an enclosure at one of the big box retailers for well under $500. The price might be great, but the downside is that they are not very durable or safe. Particularly if you have teenagers or pre-teen children. Compared to a good quality trampoline, the cheaper trampolines generally offer poor bounce, balance, and control as well as inadequate safety.
Is it worth paying less now if it could mean paying more later?