You CAN buy one of those ready made cleaners if you don't mind throwing money away. It's kind of like paying for already mixed anti-freeze, you're paying for water.
All cleaners are a detergent, a surfactant, and a carrier for the two. I have found that a 33% Simple Green Concentrate, 33% Isopropyl Alcohol (98%), and 33% tap water to be most effiecient and the equal of most pre-mixed cleaners. Give it a try.