Well, if you're paying for a blog, shouldn't you have full control over what you post in it? Having blog moderation after being charged a fee is silly. SILLY I SAY.
And the whole thing costs $50, but you'd initially consider charging $15 per person for it? You'd get your money back after 4 people joined. I mean, if there are no maintenance costs, why put it so high? Sure, $15 won't break many people, but it is certainly a deal breaker for most of the people you're asking. If you implement this, you can be sure at LEAST 20 people will do so, regardless of cost... so why not break the price down to a minimum? I don't imagine the site to be in such dire straits as to make these fees necessary. Heck, if it's only $2 or so, people may even get the wacky idea that you're giving them a deal. How can they afford NOT to?
But frankly, something like this may as well be free. If someone's willing to make a blog on your site, they seem pretty set on supporting you. A registration alone or something will dissuade random asshats (at least those with little to no comittment). Blogs are a dime a dozen, and should cost as much. There are plenty of other music sites that discuss the industry and techniques, and though this is certainly a unique site for its specificity of genre, people can certainly get their kicks elsewhere.
That said, I wouldn't want one, and I wouldn't care to read any.