Agree about rain, leaving the charge door slightly closed, as far as it will close with the J1772 connector in place, seems to enough for the rain but something like that might be nice(but WAY overpriced) to help with blowing snow, that tends to fill up the area around the charging port and when you unplug the J1772 connector it can get inside the connectors and leads me to blow it out with compressed air or my battery leaf blower if I want to spend the time digging it out.
As far as something cheaper, someone from Canada posted something similar but it used nylon instead of hard plastic and it was more specifically meant for snow. I believe the nylon thing could be left on even while driving, unlike the plastic thing linked.
I don't remember the price of the Canadian cover but it was more than I wanted to spend but I don't think it was outrageous as that plastic cover coming in at over $373 USD
(wow! the pound is sure low, I remember when it was almost twice the dollar!)