Lots of threads about boosters ... They do work, but it's a mixed bag.
There are single-phone boosters far under the price range you're looking at. 400-500 sounds like a repeater, designed to service multiple phones at the same time.
A place to start, with your Jetpack would be hooking up an external antenna mounted to your ladder / roof. The three older Jetpacks I've had all had two antenna connectors on them (including the Walmart StraightTalk one). Hook up one or two antenna and see how that does.
If nothing else, you can use the antenna with the booster / repeater you buy, as they generally come with a very basic external antenna.