Flying to YGK is indeed an expensive proposition.

Your best bet is to fly either to Ottawa (YOW) or Toronto (YYZ) and then rent a car or take a train to Kingston. Unfortunately neither YOW or YYZ are adjacent to a train station so you will have to taxi it to the appropriate station.

If you are coming from EWR your cheapest flight option may be YYZ, with either a rental car or train. No low cost carriers fly to Kingston.

To get into Canada you need proof of US citizenship. A driver's licence is not sufficient. Make sure you have your birth certificate with you at a minimum... a passport is preferred but not required.

Enjoy your stay.