Since these are effectively a loss leader for the manufacturers�, who are relying on the sale of the consumable ink cartridges for their profit � many cartridges supplied with new units have a reduced ink quantity. Otherwise, as Wickerman says, you could just buy another printer, rather than a new set of cartridges.
The cost of printer ownership is heavily dependant of the cost of ink cartridges, before you buy, check that cheap compatibles are readily available.