Air/Fuel Ratio Sensor - 03 Accord EX V6

Currently I have 115 kms (69,000 miles) on my Accord and the emissions indicator has come on. At first I thought it was a loose gas cap however, the indicator stays lit after tightening the cap and leaving the emissions system to correct itself for the recommended amount of time.

I took it into a Honda dealership and their analyzer indicated codes P0154, P2247 and P2254 which relates to the A/F Ratio Sensor. If I left this faulty sensor in for an extended period of time what troubles would it create down the road? What fair $ amount should I pay for this repair? Currently I have been quoted $440.00 plus tax.