I would buy some back catalogs that can serve as price guides. Catalogs are expensive for dealers to produce, so it is fair to pay for them. Usually they are cheaper than books with the same amount of information. For high-end coins you will learn far more than you can from any published price guide, and for less money, too. Fixed-price catalogs are valuable, too.
Most collectors buy coins from fixed-price catalogs.
I got an unsolicited catalog in the mail. If you got a glossy flyer in the mail from a mass marketeer with a few ancient coins offered among many other coins or artifacts, buy from someone else. They are almost sure to be overpriced. I buy lots of coins on the web. I know what to pay and how much is too much.