It's important to find a qualified instructor, because you will be paying this person to teach you skills you may need in life-or-death situations. When you contact certified dive masters, find out what agency he is certified by. Ask him about his experience, philosophies and teaching style. For example, is he willing to give special attention to someone who is having trouble?
Is he able to translate technical knowledge into memorable layman's terms?
Does he challenge students to master skills, rather than just passing everyone?

Prices of certification courses often range from $100 to more than $350. There is such a broad range because different courses include different things. It's essential to find out every last morsel that is included in a course, because that $100 course can end up costing you more than the $350 one.
Ask about textbooks and dive tables, log books; equipment (students usually provide their own mask, snorkel, fins and booties, but rental fees for other equipment--like B.C.'s, regulators and tank--are usually included); boat fees; open-water dives; and the certification card (including picture).