Yo! Just saw this thread and had to jump in because I spent two weeks in Tromso last winter geekin out over sensor specs for the lights. Tbh, while everyone loves the low-res video kings, I actually found the high-res bodies handle the fine structure of the aurora way better if you have the glass. I used to shoot Canon but the read noise on these Sony BSI sensors is just on another level for long exposures, especially in the deep shadows. I ended up with the Sony Alpha 7R IV because even at ISO 3200, the downsampling makes the noise floor look super clean. If you can find a used one for under 2k, definitely grab it. Pair it with the Sony FE 20mm f/1.8 G which is basically a cheat code for astro because the coma is practically non-existent. Seriously, the technical edge you get with that 61MP sensor when you are trying to pull detail out of the atmosphere is insane! Ngl, full frame is totally worth it over APS-C here because you really need every bit of light gathering area when the lights start dancing fast and you gotta drop your shutter speed to like 1 second. It is just amazing how much data these things capture!

Interested in this too

For $2000 budget, get the new a7c ii.

Sony a7 IV is one of the best cameras for Northern lights.

Get a used Sony a7S III.

Sony a6700 and a large aperture lens.