Not good idea because those that vac earlier will be unheypi.
If they wanted to provide direct monetary incentive, then do this:
Set a cut off date of 1st jab some time into the future
Then everyone already jab by then gets $1/day for rike maybe 30-100 days.
At the end date everyone already fully jabbed gets another $50-100.
But that will mean they need to $30-60B budget for that...