Preferably 6tb+. Just something I can grab and go in case of emergency. I know NAS and off-site backups, but this is for a specific use case. I’m open to 2.5" drives if that’s best but they seem usually pretty small. It will stay air gapped most of the time, so ssd makes me a bit worried whether it would lose data over time.
Online, you aren’t getting 6TB+ for under $100 without going used or very sketchy. The best I see at a reputable vendor like B&H Photo is a new 6TB external WD for a Black Friday sale price of $130. Just look at https://shucks.top/, what you want isn’t happening.
Watch your local Costco, Best Buy, Walmart stores - you might get lucky if they put out a palette of externals for a special price.