The R&D argument is getting tiresome to read. Apple like most other companies has an R&D budget that's constantly being deposited into by the sale of everything Apple sells. In other words, a sale of any Apple products contributes a percentage of the sale to future and current R&D research.
No one knows exactly what percentage of R&D went into the rubber band (elastomer by any other name is rubber). So yes when you break down the cost of the rubber band it probably is around $2.00. Add a couple dollars for packaging and delivery and maybe you bring the price up to $5.00. No matter how you slice it Apple is making a killing on these bands.
Furthermore once they sell X number of bands they will have paid for all the R&D and the resulting profit is astronomical. Apple charges $50 because they can get away with it. Their marketing techniques are about the best in the world. They have the ability to make anything they sell seem "prestigious".
So let's stop pretending like Apple deserves to to sell these at A 400% profit and that we should be happy for them and continue opening our wallets.
Rant/
Apples Net Profit margin for the last quarter was 23.39%
Google's Net Profit Margin for the last quarter was 20.78%
Those are within the realms of reasonableness, don't you think? It's not like Apple has 90% net profit and Google has 21%. So dig through the quarterly reports if you'd like. (I got my data from YCharts.com - I don't believe they have a horse in the race either way.)
In order to keep margin, Apple can charge $50 for an optional band purchase, bump up the price of all hardware by some amount, start charging for software or produce products of lower quality/materials for the same retail price. Generally speaking, accessories or add-ons (be it watch bands, soda, pinstripes/tint on cars) have a much higher profit margin than the main item being sold. This certainly isn't new or unique to Apple - I'm not sure why they get blasted for it all the time.