Ignoring the cost of a tape drive, tapes are cheaper per TB, yes. I wouldn’t write off used hard drives though - buying only the cheapest per TB used enterprise drives, I’ve only had a ~5% failure rate across roughly 200 drives with 2-5 years of runtime (while I’ve owned them - they usually have 4-6 years when I get them). I usually get rid of them once they hit 8-10 years of uptime (or if any get any uncorrectable sectors).
If you only need ~50TB it’s probably both cheaper and easier to just buy hard drives, even today, factoring in the cost of the tape drive. Maybe even 100TB. I’m personally backing up ~225TB off-site these days and I still find AWS S3 glacier deep archive to be cheap enough - at current prices I’ve decided the hassle of doing tape again isn’t worth my time unless I’m over 300TB.