Costa Rica is a big yet small country so great for driving to explore. The roads are pretty terrible, aside from the main highways, and especially in Guanacaste as well as going up to Monteverde. However if you don't drive the distances are pretty far so that you will pay a good 3-5x more than if you didn't drive to get around to the places you want to go.

In short getting gouged for the mandatory insurance is still better than getting gouged on taxis or shuttles. There will be terrible roads regardless. Ticos aren't the best or the worst drivers, but drive defensively and you should be fine.