A cellular booster amplifies existing cell signal to a more usable signal. I get a 10 to 30 dbm gain with my car booster. I purchased a Weboost recommended car booster 2 years ago. A real sanity saver.
Yes, they’re expensive, but worth the one time cost.
A wifi booster would be for boosting an existing WiFi signal, should you be able to connect to one that isn’t secured.