I have a small projector for home use and have always been curious about what makes the bulb used in the projector different or special from a regular bulb? And also was curious why they are so expensive compared to regular bulbs.
They are typically designed to run extremely bright; much closer to the limit where they would burn out than, say, ordinary household bulbs; this means they must be engineered to contain less flaws and imperfections in the filament, envelope and other components than would be acceptable for ordinary bulbs.
It may also be the case that manufacturers charge a lot for them because they can - you have the projector, you need the bulb - you think it’s a bit pricey, but what are you gonna do?