I have a cradlepoint AER2200 setup with an AT&T connection at a location across town at a warehouse that gets occasional use. We were going to be using handheld wireless bar code scanners that needed connection to our ERP server. I created an IPSec tunnel to our main office and used an ACL to only limit the correct ports to the server here. Anyway, the connection has been reliable even though it doesn't get much use.

They were going to move out of that location and I was happy because I was going to use the cradlepoint in the main office as a backup, but more for out-of-band management, than for the whole company. Now we have at least another 6 months at that location, so I might end up getting a new one for here anyway. We'll see.

You may not have LoS to the building from your current location but I had a similar issue with a client and we were able to negotiate with the property management of a nearby apartment building that did have LoS. My client rents access to the building roof where we installed fiber internet access and a Poit-to-Point network. There's about 2km between the PtP devices and we managed to get about 175Mbps speeds using Ubiquiti gear. Would that be an option you could investigate? Easy to setup VPN between locations at that time.