since you have the main structure, i'd glue up foam and shape it on the body. using contour gauges or cardboard templates to get the shape right and glass over it. one off parts do not require a mold. the problem with this method is that your rough side is the side you want to paint. lots of bodywork to get it paint ready, but it's doable. check out fiberglassforums.com
this is where i learned to glass my interior parts and tonneou cover.
there are a lot of guys on that site doing the same thing. you will spend a lot more time but a lot less $$$ than buying one.