From a Harper Highlights newsletter:
'Sign up to the new BookBliss newsletter and you'll find out about our daily new e-book deals, with most under $5! You'll also be the first to hear about exclusives and special offers, so sign up today — it's free and you can unsubscribe at any time.'
They maintain that there can a saving of up to 80% on ebooks - and that most deals are under $5.
Example books given:
The Alchemist - Paul Coelho
Disruption - Jessica Shirvington
Magonia - Maria Dahvana Headley
You're the Kind of Girl I write songs about - Daniel Herborn
BookBliss newsletter url:
http://www.harpercollins.com.au/bookbliss
I'm not sure that $4.99 is a bargain for any/all the books they put forward, you'd need to check other book sellers for each book that you're interested in I guess.