SBC == Single Board Computer, like a raspberry pi or similar
Some of them are a bit on the expensive side these days (150$/£/€ or more), so some people go for refurbished thin clients instead e.g. Fujitsu S920 or a Dell 7040.
The Odroid N2+ that I use, ended up costing me about a 100-ish incl. case, emmc storage for os, emmc adapter so I can put stuff on emmc using a computer, and a POE power splitter. I was buying it so I could hook it up to a TV (and get HDR10+/DV from Kodi) those more powerful and somewhat larger thin client machines can’t do modern video as well - they just don’t have the modern hardware accelerators.
This particular board I’m using comes with 3x physical 3.0 ports hooked up to a single USB root hub - I have one more port free for another drive once I run out of space (probably not soon, the 20TB disk is new - maybe I should peel off the plastic).
If I wanted more disks from the start, I’d look at enclosures: Festplatten & SSDs Externe Gehäuse mit Formfaktor: 3.5", Datenträger Anzahl: 10/12/13/15/4/5/6/8, Anschluss intern: SATA 6Gb/s Preisvergleich Geizhals EU . The ~ $250 raidsonic/icy box 10Gbps one is nice.
There used to be $30-ish nanopi neo3-lts available, it’s similar to pine64 rock64, as well as several other $50-ish boards with multiple USB3.0 ports. It seems everything has gone at least 50% up in price over the last year and availability is making shipping more expensive… see above for reference to people using thin clients.
Oh the software stack I’m using is pretty insane, it’s very much the case that when the thing reboots, I need to ssh and run a shell script to mount filesystems and start containers for fileserver stuff,… CoreElec which is is the distro I’m using for Kodi video playback, isn’t built for NAS-ing - but allows for Entware and has docker.
Basically, how much space do you need? How many drives do you want? How much random read write or sequential performance do you need? What apps do you want to run on it / other than presumably maybe samba?
BTW, good price for HDD space at home, currently as of December 2022 is <$15/TB – after about 2 years of stagnation the prices of HDD space are finally falling again.
The cheapest per TB drives are generally either the biggest drive from previous or one before previous generation of HDDs (16-18T per drive) or the second biggest drive in current generation of HDDs (e.g. 20T drives).
Tere’s several websites that track pricing like geizhals.eu and diskprices.com . Right now, it’s not a good time to buy, because Thanksgiving sales and discounts just ended. camelcamelcamel can send you notifications when price of something goes down, and you can see historical pricing too - as an indication for how low can price of something go, and you can check in on prime days on Amazon and before other holidays / or back to school days and what not.