Scanners vary greatly in cost depending on features. Choosing the correct type of scanner to fit your requirements will save many wasted hours over its life.
Scanners can be connected directly to a single PC or networked so they are available to everyone in the office. Which option is best for you depends on how you plan to use the scanner. A directly attached scanner tends to have more comprehensive software which will allow you to scan and manipulate in different ways, while a networked scanner may be better if many people in the office wish to scan basic documents/images.
Single Sheet or Multi Page
A standard flat-bed scanner is designed to scan a single sheet at a time. When it has finished you have to manually swap the pages out. A multi-page scanner has a loader similar to a printer tray where it will feed pages one after the other in one scan. A multi-page scanner can be much more costly, but if you are regularly scanning large documents, a single-sheet scanner is not practical.
Duplex scanning is double sided. Some scanners are able to scan both sides of a document in one pass, rather than you having to load the sheet in both ways. This can be an expensive option, but if you are scanning a lot of double-sided sheets, the time saving can cover the additional expense.