I recommend you look at
Indigo.ca. They have the Libra listed at $199 which comes to under $150 USD. They also had a pop-up saying if you signed up for what I'm sure is their spam list, they will give you 10% off of a $50+ order.
As for choosing between the two, I can't help. I've always stuck with 6" readers. My only reason for looking at the Libra is the waterproofing and buttons and you already said those don't matter much to you.
I don't think the Libra is all that much larger than the Clara due to the smaller bezels on three sides of the screen. Maybe someone that has both could post a pic of the two side-by-side.