Couple things to consider:
Transbridge Bus Lines has [regular service](http://transbridgelines.com/newark-airport-schedule.html) between downtown Easton and Newark Airport (EWR). Takes approximately 1.5 hours, varies depending on time of day. You can fly pretty much anywhere from Newark.
Alternatively, you can fly from Lehigh Valley Airport in Allentown (ABE). ABE is closer to Easton, but has fewer options.
One weird option is that United offers cost-effective connecting “flights” from ABE to EWR that are [actually on buses](https://www.tripadvisor.com/ShowTopic-g46671-i866-k6851911-o10-United_Airlines_Bus_Service_from_Newark_airport_to_Allentown-Newark_New_Jersey.html). Yeah, I know this sounds crazy, but it’s true. You board a United Express Bus at ABE, which goes directly to the United terminal at EWR. I think you still have to go thru TSA at EWR, but not sure. The United Bus “flights” don’t seem to show up on third-party travel services like Expedia, but you will see them if you search for flights from ABE at United.com