You know, it's hard (if not impossible) to find small hole saws for plastic... like atty size. Many of us use regular drill bits and swear a lot if we break the plastic, or we make a hole saw. You can file teeth into, say, a 1/2" thin walled pipe for larger buttons. Or use an old dead battery and file a few teeth on the end of that for atomizer connector holes. Go slow.
Dremels work for some things, a reamer helps too. Start with a smaller hole and ream it out. (so I hear... I don't use one). You get the idea........
I find I use my Dremel more for sanding and cutting than hole drilling with e-cigs. They do have a nice set of very small drill bits tho.