You can make a cheap computer without Raspberry Pi. One option is to install the Linux distribution on some ARM netbook for Android. For example, the Chinese netbook WM8650 (manufactured by WonderMedia Technologies) costs about 50 euros. It's a bit more expensive than the Raspberry Pi, and it doesn't have a good GPU, but it does have a monitor, case, battery, touchpad, etc.
One of the Linux users published a detailed description of how to install the Arch Linux operating system on the WM8650 netbook and what problems arise in doing so. Specifications
SoC at 800 MHz
256 MiB DDR RAM
2 GB of internal flash memory
Display TFT 7 "800x480
3 USB hosts
1 ethernet port
WiFi
Headphone and microphone jacks
Battery LiPo 1800 mAh 7.4V
Power Adapter 9V 1.5A
Android OS 2.2
In general, in order for Linux to work on an ARM netbook, you need to roll a few patches. The author lists each of them, so that the upgrade can be done step by step. In general, you can do much easier and get a ready-made Debian distribution for ARM, but the reviewer is definitely a fan of Arch Linux. According to him, the existing Debian distribution is not well optimized. For example, the system will boot up on a netbook for two minutes. ')
Installing Linux on WM8650 netbook: part 1 , part 2