This topic just arose on Twitter and I thought it would be useful to address two questions: (1) the cost of a single ISBN vs packages (2) the cost of ISBNs in the US vs overseas.
First, why a single ISBN costs $125, while packages of 10 or more are cheaper. Bowker doesn’t encourage the purchase of a single ISBN, and that’s reflected in the pricing. The truth is, most books are published in multiple formats these days – ebook, hardcover, paperback. And each one needs to be separately identified in the book supply chain – which requires each separately tradable product to be assigned an ISBN. So anyone purchasing a single ISBN is more inclined to re-use it for another product or format of a product – which really causes headaches to the supply chain, as it overwrites historical data and confuses retailers. We price packages of ISBNs at a lower per-ISBN price because we want to actively discourage the confusion that results in someone re-using an ISBN. However, we also recognize that occasionally, a single ISBN purchase is warranted, so we do allow for it.
It’s interesting to note that in the UK, purchase of a single ISBN is not even possible. Initial packages start with 10 ISBNs.
Second, why the cost of ISBNs in the US is higher than it is in other countries. Outside the US (and the UK, and a few other countries), ISBNs are issued by organizations with governmental support – national libraries, for example. In the US, ISBNs are issued by a private company (Bowker/ProQuest, where I am an employee); in the UK, ISBNs are issued by Nielsen. So in some countries, ISBNs are essentially subsidized by taxes. Unfortunately that is not the case in the US. You can find the appropriate person to email about that here.
I hope this helps explain things.