I'm looking at these:
http://www.amazon.com/gp/product/B006YIU5TI/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=A2RA9SXXT GVE9R
Amazon.com: Rola 59834 Mazda 5 Cross Bar: Automotive
Rails and box for under $500 and decent reviews on Amazon. I don't need them right away, but will after another 4-6 months.
I am not too worried about getting the most aero designed rails and box out there. The fuel savings over the initial cost would probably never equal out for as little as it's going to get used.