Cost-Effective Indie Backup: Beyond LTO/Cloud?

Hey everyone, Jordan here. I'm hitting a common indie filmmaking snag, brilliant creative team, but a shoestring budget. We're shooting a narrative short on an ALEXA Mini with some killer Orbiter lights, and every penny is accounted for. My biggest worry is data integrity post-shoot. LTO is a pipe dream right now, and even decent cloud storage for terabytes of raw footage is just too much to factor in. I've been doing local drives and a second copy on another drive, but I'm looking for foolproof, budget-conscious methods for verification. Are there any DIY checksum verification tricks you've used that don't involve paid software? I'm talking absolute minimum viable strategy here, just to ensure those precious frames are safe. What have you guys found works best when you're truly scraping by?