Flight
Flights from Philadelphia to Lansing are (at the time of writing) about $180 less per ticket than flights into Grand Rapids for the weekend of 9/1/19. The Capital Region Airport in Lansing is 1 hour on the highway from downtown Grand Rapids. The wedding location (in Whitehall, MI) is 1 hour further beyond Grand Rapids. Depending on your preference for hotel location after the reception or for travel time on your day of departure, staying over in either Grand Rapids or Whitehall can work using the Lansing airport.
Flight
For anyone in the Philadelphia area, BWI to Grand Rapids is about $180 less expensive (at the time of writing) than PHL to GRR. This is an alternative to flying PHL to Lansing, MI. Driving two hours from the Philly area to fly out of BWI will land you in Grand Rapids rather than Lansing, saving an hour of driving on the Michigan side. Depending on which you think more convenient, either would be a good option.
Flight
Rental Car