This is the cheapest Kindle offered currently and goes for $69-89 new on Amazon.
The "pre-owned" Kindle offered here is $39. Cowboom doesn't specify whether or not this is the model without ads.
Since this is actually a site run by Best Buy, "pre-owned" probably means returned to the store within a thirty-day period. All reports I've read on "pre-owned" Cowboom products have praised the condition of the merchandise received, suggesting it is either refurbished or as-new.
Here's the link.