The split won't actually raise capital for the deal, but will help to payoff shareholders of the railroad. According to http://www.marketwatch.com/story/berkshire-approves-50-for-1... the split is to "accommodate holders of smaller amounts of BNSF shares who opt for a share exchange rather than a cash payment."

So, some shareholders of Burlington will opt for shares instead of cash, and since you can’t own a fraction of a share, they have to split the stock to accommodate them.

No, you can buy B shares at 30-1 value of A shares for about $3000.

I believe Class B wasn't introduced for that reason, if I remember correctly it had something to do with people with Class A needing to divide stock to leave it in their will or as gifts.