To answer your question honestly, I would memorize it by heart, because many english speakers do use "Look" in that particular sentence. And for the word "Find", I would add the word " Out" after it. That makes sense too. "Someone is at the door. Go and find out who it is."
And for the second sentence, all of the answers are acceptable, but you can change the question a bit too, but the one that you've used is fine as well. Another way to reword the sentence can be "The prices of books are getting () these days." Both are fine.