Do you speak German? If so, it's probably best to look on the Vodafone.de site for their taffifs, similarly for T-mobile etc. If not, searching around, you can find offers like this:
Germany SIM Card
This is more expensive than the best you can do buying a local SIM in Germany, but it doesn't look too bad. $99 for 5G + a small amount of voice is much cheaper than Verizon's international data rates. This way you would get the phone number before you left, they will forward 2 hours of calls from your US mobile number to this phone etc, so there is a lot of additional convenience.
But if you or your family members are good at German, wait until you are there! (That said, one of my daughter's friends who was fluent in French said that her most challenging time of her year in Paris was signing a mobile contract. Apparently school French doesn't quite prepare you for that!)