Is Costa Rica expensive?

In short: yes, Costa Rica is pretty expensive, especially compared to most other Latic American countries. 

A week of vacation in Costa Rica costs between 850 and 1,450 USD for an average traveler in mid-priced hotels, lodges or rental houses and doing standard tours (assuming double occupancy). Beachfront accommodations and high dollar activities like deep sea fishing will quickly push the budget over 2,500 USD. On the other end of the spectrum, backpackers can spend as little as 250 USD a week for a dorm room and a plate of beans.

As in any country, accommodation in Costa Rica will be your main expense. Hostel dorm beds are between 5,500 to 10,000 CRC (10-15 USD) per night. Private rooms in hostels are usually around 15,000 CRC (25 USD). Budget hotels begin around 17,000 CRC (30 USD) per night for a double/twin room and go up from there (breakfast is often included). 

By eating at sodas you can expect to pay around 535-1,600 CRC (1-3 USD) for meals. Most restaurant meals will cost around 3,900 CRC (5 USD) or more. A very nice meal in a tourist area will cost around 9,000 CRC (15 USD).

Entrance into most national parks is usually around 5,500 CRC (10 USD) with discounts available for students. Canopy tours and day trips are around 25,000 CRC (40 USD). A two tank dive can be between 30,000-53,325 CRC (55-90 USD). Surf lessons start around 11,000 CRC (20 USD) per hour. 

Keep in mind, there is a 13% tax on all purchases in Costa Rica, including souvenirs, food, and hotels. Hotels add an additional 3% tourist surcharge and most restaurants include a 10% gratuity fee. You are not obligated to tip on top of this, but you still may want to tip some people while in Costa Rica, including maids, bellhops, or drivers. Tips for these services usually range from 500 to 5,000 CRC a day. Taxi drivers don't expect a tip.