I came across this one today, good specs, it's on eBay but the guy is selling close to 2k units now. I looked at the seller's 7 inch tablet has a dual core for $99. Not related to him btw as always caveat emptor.
Jeez! That even has an ethernet port on it.
Anyway... What comes to OP's question, the cheapo tablets are a bit hit and miss. Processors on them seem to vary between 1 and 1.2GHz and memory is usually 512MB, so none of them are what one would consider lightning fast.
Google Play seems to be missing from pretty much all of them. Except on the $69 Azpen at OfficeMax. Or at least it shows the icon on the picture. I ordered one of them, so seeing is believing. I might actually even stop by OM B&M tomorrow morning to check and see if I could get one from there.
Amazon has a lot of apps, too, so missing Google Play might not be a big deal for your mother, though.