TBH, you need additional backups anyway and you don’t need 100% uptime. You don’t need to pay much for it for internal redundancy (aside of storage) and server features.
Buy the nuc, buy one or two 10GB HDD with usb/usb-c and an external case and your are good to go.
But in the end, any PC will work. Get a cheapo PC, buy 1 SSD for the os and container and a big external disk for storage.
I’m running a Ryzen 5 5600G with 32GB Ram, B450 Chipsets, 1TB SSD for internal and 2 4tb SSD for storage in a micro atx. Cost me around 1200€ bucks 2 years ago.
You can even use an old laptop with a broken panel if you like.
Another possibility is, to buy a cheap (old) server from some company renewing it’s support contracts (loud, space, power hungry).
Or buy an fanless industrial pc. Anything is possible. You could even try to use arm.
I’d recommend to optimize for power consumption, noise (depending where it is located in your home) and storage. Not ECC or redundancy. as long as you do regular backups to another system, which you should do in any case, there is no reason to pay double for something.
First thing I bought after my system was running, was an additional nic, to be able to use the server as a firewall, not an UPS or another hot standby PSU