I know what you mean, I don't mean to put off racers with not much experience etc. Just there are some bully racers who are about and also those who would want to join just to wreck peoples races for a laugh, purposely driving badly etc. They wouldn't bother if it cost them money, the'd find a free league to mess about in.
Obviously I don't want to spend money, I'm not rich but sometimes it's worth it. Imagine going into bar, if you want to stay in the free area with all the casuals who get a bit drunk, shout a bit too much start fights then you can, or you could pay a little and be part of a more exclusive but welcoming private area for people commited to the sport.
Just an idea though!