Is it still under warranty? Should be, if less than a year.
Now, I've no way of knowing if they're as customer-friendly as Amazon, but if it was a Kindle, likely Amazon would either go ahead and replace it for you at no charge (even though it's not a 'defect' but rather 'damage') or offer you a good discount on a replacement device.
Still, I'd suggest contacting Kobo directly and see what they say.
I doubt Best Buy will do anything unless you purchased an extended warranty from them.
And, FWIW, I'd never put it in my purse with out a case or cover.