Low cost console servers

Hi r/networking

I work for an SMB, and I’m looking for some low cost ways to add some out of band access to my branch offices. Most all of them only have a router and 2 access switches. (Some have more, a few only have one).

I’m looking to add some OOB access to the console ports on the gear. Unfortunately I won’t be able to have a secondary internet connection, but I do have access to POTS lines at each site. My intention would be to use the primary internet circuit for console access to the switches, and if need be the POTS line for access to the router’s console. I do see there is a lot of these devices that offer LTE, but I’m not sure that it’s something I could swing management on at this time, but the option to add it later would be nice.

Does anyone have any recommendations in this space? As always cost is a big constraint, but on the flip side, I didn’t want to go try to find a low cost product and end up regretting it later either.