I wouldn't replace your home connection. You're looking at at least $50 month for just the computer, and that gets you about 5gb of data, which most anyone will burn through in a couple days with moderate browsing and YouTube. Its fine for a secondary connection, but not primary.
I can also bet you could get that Centurylink bill way down. I used to work for them when it was Centurytel, and did a lot of develppmnt work on the billing system. You should be able to get DSL without phone service, or dump the extra features and run bare phone service.
You wont get down below $91 for your phone and internet over cellular anyhow, especially if you go smartphone.