LEDs themselves weren't all that much more costly than the typical pilot
 lamp.  I recall sending $1 cash to Montsanto and receiving 2 red (was
 there any other color?) LEDs in return in 1969. 
Is there a good reason why filament lamps were used on minicomputer
front panels until the mid 1970s? Things like the PDP11/45, Philips P850, etc
all used filament bulbs, not LEDs.
-tony