Walmart has an exclusive deal with T-Mobile for their WiFi hotspot device. It is pre-paid, no contract, okay to skip months for up to a year, and supports up to 5 computers or tablets at a time. It's very fast when 4G is available (using it now), but gets slow on the older data formats it supports in some areas.
The regular rate is $35 per month for 3.5 GB. The deal through Walmart is the same $35 for 3.5 GB, but you get 2 months of usage time. To get the deal, you must purchase the T-Mobile hotspot device at a Walmart store. When you go to pay for air time, the device is automatically recognized for the 2 month deal.
Check T-Mobile's coverage map, to see if it includes your travel areas.