Chromebooks are Google's baby, and they design them to get you to use Google Apps and Google Drive (i.e. store all your documents on Google). Depending on what your dad does with the computer, this may not actually be a bad thing, since it takes care of the backup problem for you. But Chromebook + external HDD usually does not work very well.
Decent laptops (i5, 1TB HDD, 1920x1080 IPS display) show up on sale for about $500 every 2-3 months. I'd suggest monitoring this site for any deals which might pop up in your price range.
http://slickdeals.net/deals/computers/
Avoid the Cowboom deals unless you like taking risks. Many of them are used/refurbished and in worse than stated condition. Manufacturer refurb are usually pretty safe, though the warranty may be shorter. Also avoid the 3200x1800 displays, as most of them use a pentile pixel arrangement that's not really pentile (RGBW instead of RGBG) and suffer from lower resolution, bad color reproduction, and high power consumption for a given brightness.