golf umbrella from wally word for around 15 dollar.
I keep a large lawn and leaf garbage bag around. If it rains, my range bag goes in that. I also keep a zip lock baggy around, and that goes over my gun when it starts raining. I have a lightweight raincoat, but it's really hot to wear.
I had the most amazing luck for about 4-5 years, but you're going to get rained on eventually.