If you are looking for an inexpensive Windows 10 laptop you can use as a dedicated backup computer (as I mentioned in my previous post regarding a cheap, reliable backup system) then check out the open box and refurbished ones available on Blinq.
In this price range, you are likely to get 4GB of RAM and 32GB of flash storage. So be sure to get a 32GB USB 3.1 flash drive (or bigger) to supplement the meager internal storage. It will be necessary to install some of the larger Windows updates.
And if you want a laptop with better specs that can be used as an everyday computer by someone, look for something in the $300 range with 8GB of RAM and 1TB hard drive (like this ASUS).
If you are putting together a backup system, you can get a discount on 4TB portable hard drives too if you shop Amazon Warehouse for returned items. I just picked up a couple WD one for $85. So total cost of a 4TB redundant backup system is less than $300; not bad.
Note: I updated this post that was originally about a specific deal on a specific laptop to be more generic and therefore more valuable going forward.