Well, I have one that is cracked in the front of the overhead and the glass shop wants about $70 to cut a new one. It should be laminated glass just like a windshield.
The issue is that the glass shop won't remove or install the glass, I have to do it myself. They said they stopped doing the repairs on motorhomes because of to many claims of leaks.
Either way, it's not that big of a deal to remove, I just haven't been motivated enough to do it.
But basically, if it's facing forward it should be laminated glass, if it's a side or rear window, tempered safety glass is fine (and a little bit cheaper).