The local currency in Costa Rica is the Colon (with the abbreviation "CRC" and the symbol "₡") or Colones in plural. Although dollars are frequently used in the tourism sector, the colon is the currency used and preferred by locals in everyday life. Where in touristic areas you might be able to pay for things like groceries with dollars, do not expect this in the more rural or less touristic areas. Also note that dollar bills need to be in perfect condition. Dollar bills with wear and tear are often rejected.

Public transport like buses are cheap and usually paid in cash and local currency to bus drivers unless you buy a ticket at a main terminal. My experience is that you are always able to pay in colones, but not always in dollars. While in the tourism sector, prices for things like excursions and tours are usually displayed in dollars, it might be cheaper to pay in colones in terms of exchange rates.  

Credit cards from Visa and Mastercard are widely accepted in Costa Rica by stores and ATM's, debit cards might give more issues. Banco Nacional and BAC work best, while BCR and Banco Popular are known to often give issues with foreign cards. Make sure you do not wait for the last moment to get cash from an ATM, so you have time to try different banks when your card is rejected. 

Make sure that your cards are set to be able to use them abroad. You might even want to check and inform your bank that you are travelling to Costa Rica, to avoid that your card or transactions will be blocked due to unusual payments in a foreign country, which your bank might flag as possible fraud. This happened to me when I first used my credit card in Costa Rica, and you don't want to go through the hassle of having to contact your bank to clear things up. 

When it comes to tipping. Restaurants charge a standard 10% gratuity or service fee. Paying an additional tip is not common, but if you are very satisfied, you can always do that. For guides, 10% of the tour price as a tip is considered normal, housekeeping about $2 dollar tip per day that you use the accommodation.

Costa Rica is relatively expensive compared to other Latin-American countries. Staying in mid-ranged hotels or high-end resorts, eating at restaurants, booking tours, buying some groceries and cosmetics can add up quickly and might come close or equal to what you would spend in Europe or the United States. There are ways to lower your spending. For example, you can eat at sodas and stay at cabinas. The food at sodas is delicious and cheap compared to restaurants. The general impression of this kind of budget accommodations in general is that they are clean and comfortable and a great option when you spend your days outdoors exploring nature and beaches. Another option to reduce your spending is to eat and stay in lesser touristic areas. A third option for a cheaper vacation is to avoid the peak and high season.