Like all enterprise software, it's all negotiable. What gets at the heart of the question is an ability to estimate the volume. Dynatrace is measured by # of sessions & synthetics.
One user session costs 0.25 DEM and is measured as a user interacting with a monitored app for up to 1 hour or 200 user actions, if I remember correctly) (confirm with your salesperson). Do not confuse a session with a user action (i.e. user click). If you have session replay enabled for the transaction, I believe each click maybe a DEM, not sure. We are interested but have been hesitant due to compliance concerns and trying to get the RUM set up.
Synthetic cost for DEM is per transaction so if you run once per day = 365/year. If you run the same HTTP twice per day = 730/year
For simplicity, I will provide an example below of running 1 per hour.