The problem is simply one of cost with mobile broadband, so expect to get hit hard, and expect to tell people that they're not allowed to do any video watching or social media while on the clock because you're going to have to shell out close to $10/GB on nearly every major network but T-Mobile.
The cheapest/easiest will probably be picking up an UNLOCKED AT&T Novatel MiFi 5792 (Liberate) for around $60 on Ebay, pick up a new AT&T SIM card for the device and activate a GoPhone Mobile Hotspot account, and probably go with the $75/month for 8GB with $10 per extra 2GB above plan. That is probably your cheapest and easiest solution with the lowest up-front cash outlay and highest equipment price return on resale.
Technically, T-Mobile prepaid has far cheaper hotspot data (if T-Mobile is even an option in your area), but they've very recently started taking to re-farming all their high speed data network bands, and all of their used/unlocked WiFi hotspot devices that support their current 4G LTE bands are not plentiful currently and are fetching a pretty penny right now (such as the ZTE z915), but probably won't stay that way by year's end. It might be a judgment call on your part, though, as $50 gets you 7GB of data, and $70 gets you 11GB. The savings on data versus the device cost in those 3-4 months might be worth the offset if you get solid T-Mo coverage inside the warehouse, though.
