If you go the "buy" route - the cheapest phone they are selling at the Digicel store by Burger King is 3500JMD (apx $45US?), plus 1100JMD for a 30 day international plan and local time (200-1000JMD).

If you return regulary, even year to year its probably worth it to buy one. But if you are staying 2 weeks or less I don't know that you'll get the best bang for you buck with the International Plan...depends on how much time you spend on the phone back to North America. Even with "local" minutes you can talk for a decent amount of time, rates are cheap.