There is no entrance fee. They have maps at the Visitors Center at the front gate. See fact sheet here (pdf file).
The refuge's Headquarters/Visitor Center is east of Houston. It is located on FM 563 approximately two miles south of I-10 (exit 810).
See the maps section of the refuge website for additional directions.
The address is 4017 FM 563, Anahuac, TX 77514.