These reviews may help:
The bulbs are not cheap and I've seen prices as high as £300 for replacements...:-(
Incidentally I regularly watch various TV programmes on a 72in drop down screen displayed by a quite small Toshiba overhead TV digital projection unit.
The full screen picture (and sound) quality is, frankly, utterly stunning.
However, a new projection bulb when needed is about £500 (less with an internet search).