Best inverter for 4 desktop pc's

I have a small office and have 4 desktop computers in the office. For the past couple of days there have been a lot of power cuts and the use the computers in the office is a must. So I require an inverter which would allow four desktop computers to work for at least 4-5 hours. Please advise which inverter would be the best for this use.

It would be good if you give a cost so something suitable can be suggested. Otherwise there are many inverters which all have a different price range.