I'm not always Kinko's biggest supporter, but I do work there. I'm one of the production guys that runs the giant inkjet. The Deskjet really does do some nice prints.
The "back-lit" material works best for the marquee. It's $15/sq ft, but all of the old pricing states that there is a $25 minimum charge that they may enforce. This is what my marquee is printed on.
The "indoor banner/polypropylene" option would work well also, but the material is more opaque. Colors will be washed out a bit due to the white background material, but you should get decent results. It's $7/sq ft at most stores.
With the dimensions you stated it'll only be 1 square foot.
It's $15 a square foot. If it overflows into 2 square feet they'll try to charge you another $15 but don't let them - they can break it down to actual print.
With the new POS system that started in October of 2005, there is no way to enter in a partial square foot. We enter in the dimensions of the print, and the computer does the math and charges by the full square footage.