You can get individual pagess printed at Kinko's, but they'll be $22+ for 18" x 24".
If you plan ahead and can deal with the UPS ground shipping, Shortrun Posters might be a better alternative. They have flat-rate shipping of $10 for any size order, and posters are $2 each at their lowest price. I just placed my first order, and their online system was very easy.
The only things to remember when sending things to them (or Kinko's for that matter) is that output size and resolution matters. Shortrun's output is at 17x23, and they suggest a minimum of 150 dpi at that size - 300 dpi is best.
They accept many different formats, including PDF, so as long as you work with the end size in mind, you should have no problem.
If you don't have any MindMapping software yet, you can either go to bubbl.us and use their web-based software or do a search for FreeMind on Google - FreeMind is an open source program that will do most everything that the commercial programs will.
If you have any suggestions for other things to "super-size" in your marketing efforts, let's hear them!