If you just feel like taking a stroll, the park is free (Sunday 20 FF) and the scenery is better the further you go from the palace. There are even informal groups of trees near the lesser outcrops of royal mania : the Italianate Grand Trianon, designed by Hardouin-Mansart in 1687 as a "country retreat" for Louis XIV, and the more modest Greek Petit Trianon, built by Gabriel in the 1760s.
More charming and rustic than either of these is Le hameau de Marie-Antoinette, a play-village and farm built in 1783 for Louis XVI's queen to indulge the fashionable Rousseau-inspired fantasy of returning to the natural life.
The park is extremely large. If you find that you cannot manage them by foot, a small train shuttles between the terrace in front of the château and the Trianons. There are also bicycles for rent by the Grand Canal, itself a good fifteen minutes' walk across the formal gardens, and boats for rent on the canal (aroumd 55 FF for 4 people for lhr).