While personal copiers are the least expensive, offices that do even a moderate amount of copying will appreciate the features a better machine can provide.
To start, look for a model with a paper supply of at least 250 sheets. A 500-sheet supply is even better and typically isn't much more expensive. If you expect to copy multipage documents, nothing is more important than an automatic document feeder that will enable you to start a job and then leave the copier to do other tasks.
In terms of performance, look for a copier that can produce the first copy in under 10 seconds. You should also get a model that doesn't require any warm-up time, particularly if you expect usage to be in fits and starts.
One great value on the market is the Xerox WorkCentre XD 105f digital copier. It includes an automatic document feeder, as well as full reduction and enlargement capabilities on its small 20.4" x 19.3" x 14.9" frame. The Xerox is also pretty quick for the price, offering 10 ppm for less than $800.
A second choice is the Canon PC745 Personal Desktop Copier (19.1" x 17.3" x 11.3"). It costs about $100 more than the Xerox model but also offers a bypass tray for making transparencies or copying onto thick sheets of paper.