Do you know about Costa Rica's Little Dry Season or Indian Summer? It's called El Veranillo de San Juan and it is a weather phenomenon, interrupting the green season (rainy season) for one month of glorious summer like weather. This phenomenon occurs between June and July so it's a great time to take advantage of prime weather with low season prices!
Hotel rates drop by more than 25% during this period! The country is green and verdant thanks to the onset of rain in May and the beaches are much less crowded than they are in December, January and February. Hotels and lodges are likely to offer specials such as an extra night for free, and resorts that are almost impossible to get into during the dry season are available and with much more attractive prices.
In so far as driving in Costa Rica is concerned during this period, opt for a private transfer. You'll be glad you did, since many roads suffer inconvenient interruptions such as landslides during the rainy season, so having an experienced Costa Rican driver navigate alternative routes is a real blessing. Domestic flights in Costa Rica operate during the rainy season but your best bet is to book a flight that leaves in the early morning. Chances are the weather is better in the morning than in the afternoon no matter where you are in Costa Rica.