The Osa is remote. There isn’t much civilization here, nor a lot of agriculture – supply and demand, rough roads, long distances, etc. mean that generally you will find things more expensive here than in other parts of Costa Rica.
While we too wish things were less expensive, we are really happy that we aren’t living in Jaco or Tamarindo, where yes, things would be less expensive, but then we wouldn’t live on a deserted six mile beach, or be able to hike for 30 miles without seeing a soul.
Staying on the Osa, you are paying in part for all that remoteness – vegetables have to arrive all the way from San Jose (and sometimes they don’t arrive at all) – they cost more, not to mention fuel, motor parts, light bulbs, you name it… So, FYI, if you are somebody that wants a “great deal,” you will definitely find travel less expensive in other parts of the country.