ESF is a HL modification
HL is a action game, action game's don't require a payment 4 playing, cause everybody can host server's (4 free)
only Online RPG's like ragnarok (
http://www.ragnarokonline.com ) require a payment, cause there is just one server who have too be paid 4.(without payment the server couldn't stay online)
in other words: ESF don't require a payment, u just need HL, CS-Retail or blueshift standalone