Yeah, you could buy an Exit Quick Trip once you reach Center City.

Or just pay the conductor cash ...

Ways to Pay

>SEPTA accepts cash for travel on any Regional Rail line. Exact fare is not required. The conductor can make change, but bills larger than $20 are not accepted. The cost of the trip is higher when paying cash on board.

... which in your case (Paoli being in Zone 4) it'll be ...

Fare Pricing

>Paid on Train, Weekends/Evenings: $7