Apple's Memory Storage Rip-off

What is the true cost of memory? According to Apple, it's very expensive. The iPhone, iPad and iPad mini come in 3 memory storage capacities: 16GB, 32GB and 64GB. The devices are otherwise identical. The table below shows the pricing of the iPad for each capacity:

Apple's on-cost for increased memory is consistant across all the device ranges:
16GB --> 32GB: $100.00 equivalent to $6.25/GB
32GB --> 64GB: $100.00 equivalent to $3.13/GB

However, if we look at the cost of SanDisk Memory Cards, the on-cost is much less (from Amazon.com):
16GB --> 32GB: $10.00 equivalent to $0.63/GB
32GB --> 64GB: $30.00 equivalent to $0.94/GB

This is an incredible rip-off! Based on the above, Apple is charging 1,000% more for the step up from 16GB to 32GB than SanDisk do on Amazon.com. And I'm not even using the sales prices quoted on the site. I know this is not the most accurate way to calculate what memory actually costs, but I don't have access to Apple's BOM. I also have enough understanding of marketing to understand that products are sold at what the market will accept, and that product range steps are artificially created to create demand. However, I personally think that $100.00 for 16GB or even 32GB is way more than it needs to be.

Thanks for reading.