Almost all Costa Rica hotels work 3 seasons: low, high and peak, with significantly different prices.
The peak season is Christmas week, New Year's week and the Holy week aka Easter weak, where occupancy is usually close to 100%, so it is convenient to book in advance so you know your budget and you get a place you want.
Like most others, our LOW season is usually the months of May, June, September, October and 1st half of November
The HIGH season is the rest of the year, specifically: July and August, 2nd half of November, 1st half of December, the rest of January, as well as February, March and April other than whenever Holy/Easter week falls that year.
Many years ago July and August were not part of the High season, but the increase in tourism from Australia travelling in their winter and Europe traveling in the summer of the northern hemisphere has caused the high season to now include July and August.
The picture was taken in the rainy season – during the month with the most rain. The car you see there was not cleaned or doctored for this picture. While the roads had lots of potholes and mud, this car had in the past 2 years no problems making it.