Yeah, they’re tough. My wife and I do them together and can usually do up to Wednesdays without too much help, then things get ugly.
My local thrift store! I usually find at least one good book 50% of the time, and sometimes I’ll find 3 or 4 that are on my to read list. They’re never about $3-$4 each too, which is great.
If it helps, I read the ID Software book a few years ago and it was great.