The price you pay is the going rate for the shares on the NY stock exchange and you must buy 100 in your name not say a business or super fund. Then there is brokerage which varies.
For every cruise in the Carnival group - Princess, HAL, Cunard, Carnival, P&O, Seabourne, AIDA, Costa, P&O UK and AUS, you receive OBC from $50US to $250US depending on brand and length of cruise.
If you do b2b as separate bookings then you get separate OBC for all trips.
http://phx.corporate-ir.net/External.File?item=UGFyZW50SUQ9Mjc0MjIzfENoaWxkSUQ9LTF8VHlwZT0z&t=1
I'm up to about $550 so far on a few cruises plus divs of around $30US 6 monthly.
Of course the share price you pay can fall and the exchange rate can fall leaving you with a negative result. I've been lucky. Been in twice and sold once, and profit so far on all holdings without even calculating OBC and divs. That can change.