Whip up a framework and hack up a canvas tarp to make the cover.
Zips, fasteners and awl can be found cheaply on ebay.
Mine cost about $60 to get to the stage below.
Now the prettiest canopy around - but it serves me well for summer beach trips and hunting trips out west.
Plus the satisfaction of doing all the work yourself.

bit off topic but do you have any more pics of your bar, i'm about to try and knock one up myself and that looks like what i'm trying to achieve