Any private school, even in the DC metropolitan area, will not be able to pay as much as the public school system. That being said, Trinity does its best to make up for the lack of pay in other ways. You can pray with your students and talk openly about your relationship with God. Employees can apply for financial aid for their child's tuition and it is often granted. TCS is a K-12 private school so there are responsibilities outside of the classroom that add to the workload like carpool (no busses for students), seminar (a 30 minute block at the end of every day), etc.
It's a great place to work if you're able to make about 10-20% less than FCPS and LCPS.