According to ORK airport website its €3.75 per 15 minute useage
Cork Airport - Airport Charges
According to DUB airport website its €7:35 per 15 minute useage
airport_charges.html
Cork should favour Aer Lingus rather than Dublin but Dublin are probly giving EI a discount as they use them for most of flights.
Charges at SNN and ORK are realy the same but DUB is expencive to operate from.