i know you asked this a while ago but since no one else responded... we use "iGenetics- a molecular approach" in our class and it's to the point and a fairly easy to read textbook. it costs somewhere around $160 but i'm sure you could find an older version for much cheaper on ebay
If you want an overview of a subject, there's absolutely no reason for you to get a textbook. Textbooks are dense, detailed, and definitely not just for an overview.
Best bet for an overview would be to search PubMed for a well-written review article regarding the subject.