$8/ ISBN if I purchase 100. (A ridiculous $22.50 if I buy only 10) Barcodes seem to run about $10 and can be purchased individually. Heck of an investment.
Would I *use* 100 ISBNs? Not if I don't do some serious publishing. I anticipate a chapbook or two a year, and two or three coloring books. Would an ISBN made any difference? I could stick 'em on my stuff and sell them at Amazon.com if I wanted to sign up as a power seller. ($60 for 3 months and I'd probably then let the account expire) Would umph my image as a publisher, but that's not exactly the direction I was aiming. Books and coloring books and such are just a sideline to the art products stuff I do.
Much food for thought.