Does a Duo Push authentication use a lot of cellular data? My plan is limited.

The amount of data that a Duo Push request uses is very small. 500 Duo Push requests will use approximately 1 MB of data in total. This is roughly equivalent to loading one webpage on your smartphone. You may also refer to this Duo support article for more information: https://help.duo.com/s/article/1005?language=en_US