I spent a week in the Faroe Islands last year and the humidity was just relentless. I learned the hard way that when the wind is whipping salt spray everywhere, your gear is only as strong as its weakest link. I once tried a generic grip on my old 70D and the vertical shutter button started firing randomly because moisture got into the contact points... total nightmare. You really dont want that happening when you are trying to capture a sunrise in the Dolomites. Since you are worried about the weather sealing but hate the retail price, here is how I see the options:

• Meike MK-80D Battery Grip for Canon 70D 80D 90D: If you absolutely must buy new and stay under fifty bucks, this is slightly better than the super budget brands. The button feedback is decent and it doesnt feel like a hollow toy. However, the sealing is still just a thin foam strip at best. It is okay for a light drizzle but I wouldnt leave it on a tripod in the mist for an hour.
• Used Canon BG-E14 Battery Grip for EOS 70D/80D/90D: This is the actual middle ground you are looking for. You can usually find these in mint condition on specialized used gear sites for around $85. It has the proper rubber gaskets and the internal build quality that matches the 90D body perfectly. For landscape work where you are doing long exposures, the stability and peace of mind with the used official grip is worth way more than the small savings on a knockoff. You dont want to be halfway up a mountain and have your camera start acting possessed because of a cheap battery tray.

Ive been shooting with the Canon BG-E14 Battery Grip for EOS 70D/80D/90D for a long time and I am very satisfied with how it handles harsh environments. > I am constantly out in the mist and light rain and I dont want some cheap knockoff shorting out my entire camera body Youre right to be cautious. Cheap grips like the Neewer NW-80D Vertical Battery Grip use thin plastic and lack the gaskets found on official gear. They also tend to flex when mounted on a tripod, which can cause micro-vibrations in your long exposures. Since your budget is $120, I suggest buying a used Canon BG-E14 Battery Grip from a reputable dealer. It fits your price point and the weather sealing matches your 90D exactly. No creaking or power drops, and the joystick is much easier to use with cold fingers than the third party alternatives. Its just safer for those Dolomites hikes...

Good to know!

I completely agree with gramercy parkgoer. Moisture is honestly the worst thing for these cameras. I have had issues with third party electronics failing in the fog before and it is just not worth the risk of shorting something out. It is super disappointing that the official ones are so pricey but the build quality is usually night and day compared to the cheap stuff. Talking about the Dolomites tho, I was actually looking at flights there last summer but ended up in the Swiss Alps instead. The trains there are just incredible, like totally on another level compared to what we have here. I spent hours just staring out the window while eating a really expensive sandwich from the cafe car. This guy next to me kept trying to show me photos of his cat on his old flip phone for like an hour... it was super weird. Anyway sorry lol realized I went totally off topic there.

Are you using official batteries? Ive had issues with third-party grips losing connection in the cold...

• try Vello
• skip Neewer Honestly, cheap gear isnt as good as expected.