Ericeira is a small town, and most of the attractions are within walking distance from each other. Alternatively, one can rent a bicycle to get around. Taxis and buses are also available, but can be a bit pricey. One can expect to spend around €20 for transportation during the trip.
If you have more time, consider exploring nearby towns such as Sintra, Cascais or Lisbon. For a shorter trip, you may want to consider skipping some of the less popular attractions such as the Grutas da Furninha or Casa de Cultura Jaime Lobo e Silva to accommodate your schedule. If you're visiting during summertime, be prepared for large crowds at the beaches.