What is the best and cheapest way I can protect my basement from moisture intrusion?

Regardless of the type and style of basement you have you need to do two things to help control water around your home. First make sure you have a positive slope away from your home. Preferably use clay to create a slope and then cover it with top soil. The slope should move water at least 8’ from the sides of the home. Secondly you need to control the water coming off the roof. I can’t tell you the number of homes I inspect that have poor eaves troughs and downspouts. 2” of rain is one thing but when you gather up that two inches and direct it all next to your foundation wall you are putting your home in jeopardy. Trust me there is not a foundation in the world that is designed to withstand this quantity of water. If you have got away with this so far lucky you but I advise you to extend the downspouts out 8’ and farther if necessary to make sure the water does not pool up next to the house.