The Orbi looks like a good system but it's a little expensive if OP doesn't need a mesh network. If they don't mind a little extra setup, Netgear's LM1200 paired with a decent router like TP-Link's Archer A8 or Archer AX55 will save you over $100.

If you're willing to switch your cell provider, US Mobile offers pooled data plans where you can get a data-only SIM that only costs an extra $9/mo on top of the amount of data you want. Their pooled plans use the Verizon network that US Mobile calls "Super LTE". Google Fi also offers data-only SIMS with some of their plans, but it will cost a lot more than US Mobile. Fi uses T-Mobile's network for the most part and you'll get much faster speeds than you will with US Mobile as Fi has high priority on T-Mobile whereas US Mobile has low-priority on Verizon.