If cost is one of the major factors I would consider making your own - cardboard template, cut your aluminum sheet to shape and file the edges, find a friend or a shop who can do 2-3 bends for free or cheap, drill, spray paint and hardware to attach. Should be about $150 or less depending on the aluminum sheet size you need.
For that price I would probably go with the hdpe ebay/quadboss one folks sent earlier for about $150 I thought it looked good. It also looked like as long as your brackets didn't overlap with your windshield brackets it would fit almost any windshield fairly easy.