You never had to pay for OpenBSD, you could buy merchandise to support the developers. The people paying for it are the same people who always did, they're event listed on the website. The NSA did fund a part of OpenBSD, OpenSSH, for a period, but cut that funding after the lead developer Theo de Raadt made comments on how he felt better taking the funding than not, because then the money would not be spent on military equipment.