It's not a lot of shares, but it will cost you a lot.If you're looking for dividend income and you're interested in becoming a shareholder in BlackRock (BLK -0.95%) -- the world's largest asset manager, with more than $12 trillion under management -- you might wonder how well it pays to own the stock. For instance, how many shares would you need to buy to collect$1,000 annually?Here's your answer: 48 shares. It doesn't sound like all that many shares, but there's more to consider when it comes to BlackRock ...