Well... I retrofitted a whole UK house with Cat6A, about 20 runs, longest run about 25m. The walls were dot and dab construction so quite a bit harder than drywall, but a lot easier than solid. I had my electrician brother to help for a weekend to do the cable runs. It was an entire two solid days of work just to do the runs, and this is with someone with the right tools and experience plus me having already planned it carefully. It would have taken me a week to do it alone. After that it was a full week of evenings terminating everything at both ends and another couple of weekends filling a repairing the walls. Definitely not for the faint hearted!

Worth it, though, and would do it again.