It's only "grey" if the product isn't actually manufactured by the company. In this case, no one else except Apple makes the iPad, so saying they're "grey" importers is a false statement.
For an individual importing this only Custom Duties apply. So with overnight shipping (about 3-6 business days from the USA to SA) including the minimum price of $499 it's a total of $538.99, Import Customs Duty cost (It's usually around R40 but let's say R500 because we're feeling generous), I'd be paying roughly R4407.67 (which is roughly 33%
less than the quoted price, so you're right, it's not a 50% markup

) today to have it in my hands within a week. I would actually then be able to afford the 64g model of for R6506.54, if I was willing to wait a couple of weeks for delivery and not have it delivered within a week. And this all from genuine Apple retailers, none of these so-called "grey" ones (actually got pricing from amazon.com)
I'm pretty sure more or less the same duties are applied to when a business imports bulk (which would save on shipping costs) but I might be mistaken. However, this country has a culture of "OMG, we're sooooooooooooo isolated from the world, and with the rand flucuating so much, OMG! We can't charge anything less than 50-100% markup or we'll be out of business" is BULL****. Profiteering and greed. That's where it's at in this country. Want to argue? Look at our dear leadership (both now and "tomorrows") and tell me I'm lying.
I really fail to grasp that importing products in bulk COSTS more to import including duties + vat that they want on top of their markup? I could phone 3 shipping companies right now (well, probably tomorrow or Monday?) and get quotes from all of them that would prove the more I ship (or import, for example via container) the better the shipping price I'd get. But no, greed is what drives this country... not proper business and competition. It's a "I want to nail as many people as possible for as much profit as possible because they don't have choice" type situation...