Projector prices have dropped a lot in the last few years. But the cost of replacement lamps has not followed suit. However some lamps are now below $300, most are in the $350 to $400 range and will continue to be for the foreseeable future. Therefore more and more clients buying entry level projectors are shocked to discover that replacement lamps can cost as much as half of the projector’s original price. Projectors are not like televisions that can run without any maintenance. They need to have their lamps changed on occasion, and most have air filters that need to be cleaned every month or two. Certainly longer lamp life can mean lower cost of ownership.
For those thinking of buying a used projector to save money, a bit of caution is warranted. There is usually no warranty on a used projector, and the lamp is likely to be almost expired unless the seller specifically guarantees you a new lamp
Projectors are not maintenance-free. But as long as you are aware that replacement lamps are not cheap and you will need one on occasion, you can usually budget for them over the life of your projector without it having any serious unexpected impact on your finances.
Source: http://www.focusedtechnology.com/cost-of-projector-bulbs.html

Almost all home theaters and business organization depend on UHP lamp. These are lamps that use mercury. In projector you will see them called UPH (ultra high pressure), or any of a half dozen plus acronyms. Trying to tell them apart by the different names, is mostly a waste of time. UHP, UHM, NSH, UHE, etc, are the same thing, in almost all cases

Another type of lamp are very high end, and extremely bright projectors, and its totally different. They are Zenon lamps. Comparatively Zenon lamps have a better colour range that mercury lamp (UHP). They are expensive and have very a shorter life when compared to UHP lamps. They tend to start at over $1000, and typically have a lamp life of 500 to 1500 hours compared to UHP lamps good for 1500 to 5000 hours. They also are usually only found on projectors that sell for more than $10,000