Add Multiple phone lines and pricing?

I am trying to not call and spend time on the phone, but I have 3 phone lines overall, but only 1 is with Xfinity Mobile for $40 a month unlimited.

I dont need unlimited data on all 3 lines, so what is   THE CHEAPEST WAY    to add the other 2 lines, but only 1 with unlimited data?

The other 2 lines mostly need voice and txt, limited data.

I am trying to "figure out" what the total monthly cost will be as I might need to move 1 line in the next 2 weeks.