I needed a cheep and easy way to mount a computer under a table – some aluminum stock, Velcro, and bolts made for a quick and dirty mount for around $12.00.
The aluminum stock was bent to shape in a vice and 1/4" holes we drilled for the 1" bolts.
Velcro squares were used to keep the computer from moving around.
Rip-ties were used to keep the cables under control.