If you have good cases for the instruments, one option is something like this in the case. I use this particular one for my violins and its worked well so far as long as you keep the case closed as much as possible. However it won't be as effective if you have a mesh or a more breathable instrument case.
I use Boveda Humidipacks. I have two of these in my case at all times, and usually three in the wintertimes. My case isn't very well sealed for humidity, so I go through them quick in winter. They're great and I highly recommend them.
Other things you can do are:
Biggest issue for guitars is rapid temp and humidity change. If I were you, I'd put the guitar in it's hard case along with one of these.
That will protect it from humidity. Then I'd go to your local UPS store, box it up, and ship it to a friend/family/neighbor. Tell them to put it in an interior climate controlled room (i.e. not out in the cold/heat) and not to open it. Put shipping insurance on it, so if something does happen, UPS will buy you a new one.
I've shipped 3 guitars this way and haven't had an issue.