US Air is offering some nice new deals to Belize from late July through late October. Tickets must be purchased by August 1, and obviously restrictions apply.
Sample RT fares (plus taxes and Belize's exit fees, which typically add about US$80 or $90):
Charleston, SC: $309
Columbus, OH: $309
New York: $299
I've flown the non-stop from Charlotte (CLT) many times -- it's an easy flight under 3 hours that gets you into Belize City in the late morning, so you have time to get to Coro, Placencia, Cayo, San Pedro, or elsewhere while there's still plenty of daylight.