Check a third row seat out of a Dodge Caravan, Plymouth Voyager Etc. I found one at Pull-A-Part for 38 bucks complete with seat belts. It's 46 inches wide and fits in the cab nicely. I haven't fabed it in yet just set it atop the fuel tank pedestal. I was lucky to find one in vinyl but it's maroon and recovering it will still be cheaper then the glide.
