Soil pH affects the availability of soil nutrients to plants. It is the first step in knowing if you need to provide additional nutrients and how much to apply. If you want to improve your plant's growth or understand many problems that may be harming your plant it is necessary to know the pH of the soil in which the plant grows. If you are going to apply any fertilizer it is important to know how that fertilizer will be available to the plant. A good digital pH meter will probably be more than $100. Many cheap soil pH meters are almost worthless and might give misleading results that could cause you to harm your plant by misapplication of fertilizer. Your county extension will almost certainly be able to test your pH for free and test for different nutrients at a minimal cost. Be sure to take several samples from different areas and depths.
http://solutionsforyourlife.ufl.edu/hot_topics/agriculture/soil_testing.shtml