The two parts most likely to fail in projectors are the bulb and power supply, but both are fairly easy to replace. Most projectors are phased out when the price of the bulbs becomes exorbitant or they are hard to find. Since you can still find one for $45 like scout found, you should probably take a chance on another bulb if you are still okay with the quality of the picture. Definitely plan on replacing the projector after the new bulb fails though because other parts will start failing.
Also, the age of the projector in years isn't as important as the average usage in hours.