That’s interesting! How much does it cost to buy a membership? Is it yearly? Do all parties cost the same and what does your money buy for you? I’d never heard of this before your post. Thanks!
For the most part, the cost is more nominal than anything else. It just keeps the slightly less-than-serious party members out.
It doesn’t raise very much money overall, but it keeps the slightly less-then-serious from joining. The exact process differs with each party.
http://en.wikipedia.org/wiki/Leadership_convention
Membership in any of the major parties here is $10/year, which guarantees a steady supply of junk mail. One trick is to join a party you don’t like, because the cost of mailing is more than the $10.