Since there's enthusiasts in this thread: I have a working SE/30 in storage but the monitor light is dead. What would be the simplest/cheapest way of fixing it?
I'd say to have it diagnosed. It could be the tube or something in the analog board. Someone experienced in repairing CRT TV's or computer monitors can help pinning it down.
Head over to the 68kmla.org forum where the gurus are, and state the precise symptoms. Also, make sure you've replaced the PRAM battery as they will leak at some point and damage the mainboard, usually beyond repair. Same for old leaky capacitors, which leak their corrosive contents onto the mainboard, causing all kinds of nasty and hard to diagnose problems.
if the display is too dim and you have verified the analog board is good, crt rejuvenation is an option [1] but if it doesnt come on at all, replace the crt.