Not much to this one - designed the case in Blender, I'll upload the .blend files as well as the STL's for anyone to use, CC3.0.  In the pictures you see that the original elbows just didn't have the strength to really be durable, in rev 2 I made those cross beams and the strength is amazing.

I printed the case using my local hackerspace's 3d printers, they don't charge for filament.  If it was your own I can't see this having been even $1 worth of filament.

I used a Samsung 1TB SSD, it's just connected with a USB-C cable and it sits beneath the pi in a little tray.  The SSD uses next to no power so the whole thing runs off the default pi power supply.  As technology gets better and better you could use larger hard drives, and not have more power draw. At the time I spent about $160 on it?  But they are already cheaper in price - you can find them for $120 or less.

The fan is a cheap little guy from Adafruit, it was about $3.50. To power the fan I just plugged it into the digital IO pins 4 & 6 (5V and GND).  I thought about adding a PWM type interface or some sort of relay to turn on when it got to a certain temp, but found the fan is quiet enough that I don't care about it running non-stop.

The pi 4 is the 4gb model, it should be around $55 but with the chip shortage I have no idea what's going on with the prices now.

All said and done you could have a 1TB personal cloud server for under $200, and no subscription fees, and you're not handing over your data to some big data mining company like the big G.