There's a decent fare posted today in the mileagerun section from IAH. Look around -- maybe there's new fares elsewhere.
If you want to go to BZE, you either need to use miles, pay an outrageous fare (highest in Central America, I've heard), or be patient and seize the opportunities when they come.
I liked the country, but I wouldn't pay a lot of money to return. From the USA, it's worth about 250 bucks, IMHO.