The Raspberry Pi 3B + is the basis.
I use a Class 10 SD card of 32GB for installation of software. In my case a Samsung 32 EVO plus of € 8.95.
I also have 2 USB sticks of 256GB. I first had two cheap sticks, but they proved to be unstable in a Raid configuration, so in the end I bought two sticks from the well-known brand SanDisk for about € 90, -. (More than 256gb would be nice, but I found that too expensive.)
The Raspberry Pi can block if the power suddenly falls away. A UPS can deal with this problem. I have opted for a Geekworm UPS HAT because it is cheap and has a big battery. In practice, this UPS only proved to work well when the PI and the UPS each have their own power supply. I solved this by a micro USB Y cable. I did some testing and the UPS does what it should do.
I first had a 5V and a 2.5A power supply, but the USB sticks and the UPS take so much power that too little was left for the Raspberry PI; (many Under-Voltage reports are the log). I therefore switched to a power supply with 5.2V and 3A. Now everything works properly.
I have the Raspberry Pi + Geekworm UPS HAT in a standard white Cyntech housing. I opted for white so that you can see the white LEDs of the UPS through the housing. However, I had to make a hole in the housing for the micro USB power supply of the UPS and a hole for the plastic toothpick that I glued on the on / off button of the UPS.
All in all, I spent about € 170 on hardware.