Four cinder blocks and a flat paneled door minus hardware, enlarge the hole from the door knob to hold a garbage drop.
Keep in mind that Keyboard height is 26” and desk height is 29”.
Standard depth is 30”.
It should be cost effective to modify a used desk with a drawer being made into a keyboard drawer.
I purchased two 2-drawer filing cabinets and had a piece of countertop cut the width of the span I wanted between them plus the cabinets. Then placed each cabinet as an end support. We can still use the drawers as well as a nice, sturdy work space.
Here is one way: https://www.hometalk.com/42190914/diy-desk-for-my-girlfriend-s-birthday