I've dragged gear through a few mountain trails and let me tell you, weight becomes your biggest enemy real fast. I started with a generic hard case because I wanted to save money, but the latches felt super flimsy. One time I dropped my bag while scrambling over some boulders and the case actually popped open inside my pack. Not fun. When you're looking at the Lykus HC-3310 Waterproof Hard Case for DJI Air 3, just make sure to check the latch mechanism carefully. Sometimes those cheaper models use plastic pins that can snap if you're putting a lot of pressure on them inside a tight backpack. The reason people talk about the foam is because if its too soft, your Air 3 will just rattle around. I found that with some budget options, the cutout for the gimbal is just slightly off, which puts stress on the motors during a bumpy hike. If you go with the Lykus, just double check that the drone sits snug without any wiggle room. Honestly, if you're hiking, is a hard case even the best move? I eventually switched to a dedicated backpack like the Lowepro ProTactic BP 450 AW II Backpack because carrying a hard case inside a regular hiking bag is basically bulky as hell. If you're set on a hard case for the protection tho, just be aware that the GoProfessional Cases DJI Air 3 Case usually has much tighter tolerances, but it might push your $75 limit. You get what you pay for with the pressure valves too... cheaper ones sometimes fail and make the case hard to open after a big altitude change.

Building on the earlier suggestion, hard cases are kinda clunky for mountains. I'm satisfied with these:

• Lykus DBP-100 Drone Backpack: Comfy, less rigid.
• Smatree Air 3 Backpack: Safer, bit bulkier.

Honestly, I havent had the best luck with those budget hard cases lately. Unfortunately, someone told me the seals on the cheaper options arent as good as expected for mountain humidity. IIRC, the foam density in the more expensive brand is significantly more reliable. Not sure if you can justify the cost, but I think going cheap on gear safety usually ends in disappointment.