Matting and framing is a pretty standard way to go, and presents the images in a conventional, formal way. This appeals to many viewing folks. It also conveys a respect that you have for your work. Not everyone would agree with all of this, and there is much variation in the thinking of presentation (note polyglot's comment). State buildings? To me it says something about your likely viewing audience (standard, extra standard). I would invest in an inexpensive matte cutter (Logan 301 comes to mind - http://www.amazon.com/s/?ie=UTF8&key...sl_t51gsdl79_b) sorry about the long link. It runs $85 to $90 and will last as long as you will.
Then go to Frame Destinations, where they can advise you on cutting cost and where. I would at least run the cost of doing this, at 11x14 and 16x20 just to see what the outlay would be. I agree with metal section framing and plexiglass glazing, although glass would likely be cheaper, but more problematic.