My kids have too much stuff. So while throwing out unused toys, I came across a lite-brite type toy.
I took it apart to find it had light inside ran off of batteries. Maybe it could be powered by a computer's PSU?
Taking an old Molex connector thing I had laying around, I cut the wires and spliced them to the 5 volt wires.
Plugging it in, using an old stand-alone PSU, (Didn't want to wreak my real PSU if it didn't work) the light worked.
I mounted the unit in the bottom of the case. The switch was attached in a hole I drilled in a blank expansion card slot cover.
With the cover put back on, the case was well lite up.
Cost: nil.
