I'm curious as to whether or not it is realistic for a pro to be making between 250k - 500k. It seems to either be you make around 50-100k, or you make over a million. Is there really any middle ground?
I'm sure there is, depending on what type of pro you are. Most pro's would make the bulk of their money from advertising/sponsors I would assume(as is true with a lot of pro sports that aren't basketball or football). A small portion of income would come from doing video parts if they are a video rider or competition earnings if they are a comp rider. So depending on how much of a household name you are, you'll make more. So if they're a rider who is a pretty big name among the snowboarding community, but not known among non-snowboarders, you'll probably make more than the average pro, but not in the million dollar range for somebody like Shaun White.
No one touches Shaun White. He's making many times more than whoever is #2 (I imagine it's Travis Rice).
I could see guys like Scotty Lago, etc. in the range that you posted, but really I have no clue. Hell, for all I know, Travis Rice is "only" in that range. It wouldn't be the most shocking thing I've heard.
Maybe a bit of a dated source, but it gives you a reference nonetheless. I'm not surprised by White, but I'm very surprised at Danny Kass on that list. I also wouldn't have put Rice at a mil either. I figured he made a lot of money thanks to Red Bull's high cost production stuff, but not THAT much. And just think that was 3 years ago.