From a construction perspective there's hardly any effort at all involved in skipping the 13th floor. Most of the time it's just relabeled as the 14th and the elevator doesn't know any difference.
OTOH, It would be much more difficult to retrofit an elevator to accommodate or avoid a 13th floor if it wasn't originally configured that way. That would involve completely new software and hardware.
It's not nearly as common to skip the floor as it was in the past, as it doesn't seem to bother people as much nowadays.
Interestingly, some elevators in China avoid any floor with a "4" in it (e.g. 4, 14, 24) because the word for 4 sounds like the word for "death."