Old vs New... basically because they can. I looked into ISBN's once too and that's not a bad price, as far as ISBN's go. I ended up using LuLu's 'published by Lulu' service, which put my name on the book, but the official publisher was Lulu... they gave me a free ISBN. An ISBN makes your book 'official' and opens up all kinds of distribution channels that aren't available to plain old ebooks.
This turned out to be a great move, because I forgot about my book but lulu didn't... it got listed on Amazon.com and sold several copies, and (completely without my intervention) made it into the iBook store and I've sold literally dozens of copies (well, 92 copies).
They hide it pretty well, but if you use their 'extendedreach' free distribution package, and if your book meets the requirements (mostly size and page count) you can get a free ISBN. http://connect.lulu.com/t5/ISBN-Distribution/What-Distributi...
Sorry to make this sound like an ad... just a very happy customer here.