Diane Duane's Young Wizards series (all nine books so far) is available in a
bundle for $39.99.
That's not too bad, but for this weekend only, so long as you're not in the United States, it's available at a 66% discount! That's just $13.60 for all nine books!
The details of the offer are
here
Direct link is
here, and use code YWBLACKFRIDAY when checking out.
And all the books at her Ebooks Direct website are at 50% off this weekend, using code BLACKFRIDAYDIRECT
I have them all already, otherwise I'd be buying them now.