Essentials is one of the most used plugin for Minecraft. That would be great if travels/flights could be paid using the credits from Essential Economy.

http://ess.khhq.net/wiki/Essentials_Economy

If I got that right, Vault already supports Essentials Eco.

Quote from the Vault project page:

"Vault currently Supports:
[...]

• Econ:
  [...]
  • EssentialsEcon"

Source: http://dev.bukkit.org/bukkit-plugins/vault/

Verified this using the Wiki of Essentials Economy you linked above, so this issue is solved.