You most certainly will want to rent a car. It's easy to drive around. Don't be deceived by just going to kayak.com or some site like that and seeing super low car rental rates. They don't include the mandatory insurance that will be tacked on. https://mytanfeet.com/special-deals/get-real-discount-rent-car-costa-rica/
We always used Adobe when we rented a car because 1. they are highly recommended and specific to CR 2. they always include all the fees/required insurance so no surprises when you book 3. we used this link for a discount: My Tan Feet Adobe Discount.