A UPS will vary widely in price depending on its size and feature set. But, it is no longer a luxury item. As a guide, a basic (offline) UPS (the cheapest kind) to protect a standard sort of system such as a PC, monitor and printer, you can expect to pay $100-$200, depending on capacity. The cost of a UPS can climb quickly however, as you add extra devices such as scanner, external hard drive or even additional computers, network hub/switch, router, file server, tape backup system and so on, as you will need to buy a larger UPS to provide sufficient current for the extra devices (or multiple smaller UPSs).
But for those who consider that time is money, a UPS can pay for itself the first time the lights go out. Remember, there's not just the outage time to consider (which could be only a second, to over an hour) but the time to recover from lost files, corrupted systems and damaged hardware.
It is almost impossible to get natural "clean" power all the time. Following are some of the problems that can plague (and destroy) our valuable data and equipment:
Surges and Spikes - basically, a sudden extra burst of power through the mains line. This can be caused by electrical grid disturbances or even by lightning strikes. This temporary voltage increase might last just a few thousandths of a second, but can push the current to your system from 240V up to a massive 1000 volts or more. Damage can vary from lockups and data corruption to total system failure and damaged hardware (CPU, motherboard, RAM, hard drive, power supply unit etc). Spikes, (also known as transients or instantaneous surges) are not as strong as surges. Being subjected to surges and spikes can take its toll on your PSU and other components over a period of time, leading to eventual failure.
Sags and Brownouts - these are usually very short-term drops in power (often characterised by the lighting dimming or flickering momentarily). During a brownout the voltage level "dips", then returns to normal. They are very common and can cause hardware crashes and occasional hardware damage, but can also lead to a range of problems that you may not suspect to be related to your PSU. This can include: your computer locks up or reboots for no apparent reason; data files become lost or corrupted; your CMOS setting has been lost; the image on your screen becomes discoloured or distorted; you occasionally get error codes when trying to read files.
Lightning Strikes - the damage potential from being struck by lighting is obvious. A lightning strike can deliver a million volts of power instantly and a direct strike can destroy even a UPS-protected system. Thankfully, direct strikes are rare, but you don't have to be hit by lightning, or even have it strike nearby, to suffer damage to your equipment. A strike several kilometres away can still push dangerous voltage surges along underground wires and to your mains power cord and your telephone line. A good UPS can protect both power and telephone line connections to your computer equipment.
TIP: If in doubt, the best protection is to simply shut down and unplug your equipment till the storm passes. But remember to unplug your phone connection also!
Blackouts - A blackout, or power outage, is when the power fails totally. Without a suitable UPS, a blackout results in immediate shutdown. The damage can vary, depending on what your system was doing at the time. If your system was idle, the damage could be little or none. If you were working on files then anything held in temporary memory (RAM) will be lost, and major problems could result, especially if the computer was updating critical system files at the time. Note, also, that in an outage, the power often doesn't cut out cleanly. Damaging spikes and irregularities can occur when the power cuts out and when it comes back on again.
Line Noise - this is characterised by small ongoing variations in the voltage level. A certain amount of line noise is normal and can be dealt with by a system's PSU. However, in some areas this can cause periodic and severe power problems. Noise can be generated by nearby equipment on the same power circuit or by nearby devices, such as heavy machinery, motors, radio transmitters etc. Noise can cause software/hardware lockups and data corruption and physical damage.