The answer may be Good Links and keyword specific link text. Three weeks ago my PR-0 site was on page 79 of Google for costa rica for sale by owner. Last night it was #9 - today it is #8 and it is STILL a PR-0 site competing against 1.7 Million other sites. I have less than 100 links, including DP links, and many are PR0 and PR1, but care was taken to assure the link text coincided with my site theme without spamming. Keep up the linking process but concentrate on "quality keyword rich link text" not securing thousands of useless links.
Very Good Job... Your domain is very keyword rich for the keywords you are probably aiming for. Plus it helps that you are going for a local geographic keyword "Costa Rica". I know that there are a lot of Americans and Europeans looking to retire there so it still might be competitive for your search terms... Then again a lot of real estate agents do not have a website or know anything about SEO.
Congrats. By the way PR doesn't have anything to do with page rank. Your site probably Google finds deserves page 1 as per quality for that search term.
to me Google PR is nothing. it just want to show to others how popular your website(s). and is very good if you still have a lot of traffics in your website(s). Google just want you to know how important your website to others in the world of Internet.