I'm from Germany used Waze in Michigan almost two years ago. Got an AT&T SIM card, you can buy certain amounts of data with their pre-paid plans. It wasn't even expensive, you should be fine with $20-30.
The only thing that's a bit weird is that you end up with a separate score of points for your account, because Waze uses different servers in the US or something. So i've got like 12k points on www.waze.com
, and like 88k points on world.waze.com.