The least expensive way to get to Culebra is by taking the ferry boat (La Lancha) from Fajardo to Culebra. Cost is about $2 per person, and it takes 1.5 hours.
"If you want to get from Vieques to Culebra, I would not advise taking the ferry. Spend the extra money and fly. There is no direct route between the two islands, you have to go back to Fajardo, so that's 3+ hours on the boat. The flights aren't direct either, but only 20-30 minutes in the air for about $70 per person. We took a late boat back to Fajardo, and caught the sunset, which was nice. "
