Pre-fold cloth diapers are often the least expensive cloth diapering option. However, since there is no waterproof layer, you will need to buy waterproof diaper covers to minimize leaks. Pre-folds do not have built-in closures, either, so you will need diaper pin or some other diaper fastener.
When you're shopping for pre-fold cloth diapers, you can tell how many absorbent layers are in each section of the diaper by looking for a set of numbers like this - 4-8-4. Each number in the series represents the number of fabric layers in the left, middle and right sections. The more layers, the more absorbent the diaper.