This answer from Frank Datzer at Allied Vaughn:
DVD duplication is done by using towers of burners to duplicate large amounts of DVDs at a time. This produces exact copies or DVD-Rs of your original. Replication actually uses a glass master to “stamp” new DVDs. This method dramatically lowers the price per unit at high volumes — 1000 DVD will run about $1.25 each from a DVD-R master.
This includes all glass mastering fees and 5 color silk screening on the disc (5th color is a white background or “flood” coat.
DVD duplication machines with ink-jet printers can be a good idea if you only need a couple dozen…they can be expensive to run – ink runs out quickly and the design is not waterproof – no sweaty hands! Kind of slow too — dependent on the amount of data on the disc.