Something to do would be to buy a Inspirion or Optiplex that uses ddr2(later models of them) or one of the first to use ddr3.
Then upgrade the processor somewhat, you can get away with spending $10-$30 on a processor upgrade to a Core 2 Quad used on amazon or eBay.
Then up the ram to 4gb.
Get a cheap ssd for $30-$50 for boot, then get a 1tb hdf for $40-$60 if they like to store alot of media, or just use the 250gb hdd that should be in it (some may have an 80,160,320. 320 is fine if they don't do too much.) But an HDD upgrade is pretty cheap, $20-$50 for it.
After that, you're pretty much done. Update the windows install, uninstall bloat, use ccleaner and its done

(except mouse, board, display, which you should have laying around or pick up really cheap, maybe even with the base pc you get)
This should cost you ~$200-$300 if you're smart about your findings.
I myself have an old Inspirion 537 that I up'd the CPU from Celeron to the highest Dual core I can fit in it for ~$9 from amazon. I'm bout to get the highest Quad core it takes for ~$30, and clean it up for a back up pc in case my main rig (i7, 760, 12gb ram, 500gb ssd, 1tb HDD, water cooled CPU) ever fails and I need to do stuff before I can fix it.
If you need help on upgrades, I've been doing this alot the past 5-6 years, getting a base model pc that's a couple years old for $50-$150, putting $100-$150 in upgrades to it & reselling it or using it as a makeshift gaming build since I use to play just low games like WoW and such at those times.
I have my Inspirion still and could sell if needed, only upgrades worth getting is ram to 4gb instead of 2, and a bigger HDD, can install Windows (7,8,10) & activate it on the HDD so you can clone it to a new drive. Has a decent graphics card for "parents." Better than onboard graphics for sure
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