Kodak Safelights were used in the 50s and 60s to provide a near monochromatic light source when developing film. I found a number that had been discarded, cleaned them up and either removed the colored filter on the glass or replaced the glass completely. They work really well with smart bulbs such as the Phillips Hue for washing walls with color, or providing a backlight for a TV.
Price: $75 (without smart bulb).
Patch Hill Forge 