According to ckyook :
wow, thanks to everyone for the great advice. I hadn't thought of
cutting a large strip of drywall in the middle--but that makes a lot of
sense. I will also look into the auger bits--maybe I'll have to go
with a combination of both ideas. Really appreciate it!

One thing to check is whether the drywall is directly fastened to the joists
or is suspended on lathe. If the latter, you won't have to drill any joists.

Cutting a slot does indeed make things easy. Except... if the ceiling
is textured, you have to redo the whole ceiling.

If the ceiling is on lathe and you can arrange the pot fixture holes
conveniently (eg: on a grid), you won't have to tear anything out.
A fish tape will be all you need.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.