$2 is a very small [annual] fee and I imagine it is very effective at eliminating spammers. I don't blame them for charging that fee considering the huge amount of spammers all forums face on a daily basis. The only drawback is that they don't get as much participation as a completely free forum, such as this one.
I'd rather have the greater participation we have here, but totally understand the reasons for their charge. Thanks to the moderators here for always being quick on their feet, banning spammers very quickly.