Cellular data is super crazy expensive... it's probably the most expensive way to buy Internet access... there's no way around the cost. And using cell data to power a WiFi hotspot means you'll be using laptops, etc, which can burn through data faster than smart phones do.
I looked into pre-pay data, and the prices are crazy. Only way to get close to a fair deal is with a contract. Lot of folks here like Millinumcon or whatever it's called, which is a reseller for Verizon's network.
I'm not sure I understand your which is better question? A jetpack is a mobile hotspot, but it's a stand alone device. Smart phones can also serve as mobile hotspots, using an app - usually this is heavily regulated and / or forbidden by the carriers.
In my opinion, budget carriers Sprint and T-Mobile offer better prices, but the trade off is poor coverage. If either carrier had as big a network as they advertise, their service would no longer be cheap. If the area you like to camp in is serviced by one of these budget carriers, you can save a lot of money. Otherwise, you'll have nothing but frustration.
2013 KZ Sportsmen Classic 200, 20 ft TT
2020 RAM 1500, 5.7 4x4, 8 speed