I do not know about the other versions but in the iPhone-version of Waze, in the "Data Usage"-menu, there is a slider to enable "Display network monitor". If enabled, a small text pops up in the top-right corner that informs you of the volume consumed by Waze in the current session. It is not a running total, alas, but it can give a good impression of your data-usage. Hint: downloading map-tiles makes up the most volume, so if you play around with Waze (zooming over your route) before leaving home (and while you are in Wifi) you can avoid most of the data-traffic.
AM for some 25.000 km² around Maastricht, the Netherlands
iPhone 3Gs / iOS 6.0.1