We fabricated a cheap cab for my neighbor's older BX with some light framework and enclosed with some "double polished" clear window vinyl. Awesome visibility and it keeps the snow and wind off the operator.
A reasonably priced ready to go "Cheap" enclosure could be had by using a golf cart rain cover/enclosure. You'd have to fab up some framework for it to drape over. Or buy a used "take off" golf cart roof that would double as a sunshade in the summertime.
Unless you can find a golf cart rain fly/cover in a size that would work for you.....by the time you finished altering one, you might be better off making one from scratch.
There's still a few months until the next snowfall.....hopefully!! Let me know if I can help you with some ideas.