Milton, I am so sorry I have taken so long to answer your question. I was out of town on 2 short trips and just found your question again today as I am way behind.
Anyway, I don't know how much labs charge for testing. I know some tests are more expensive than others and hopefully you have insurance as they will pay for what your doctor orders if the form is filled out correctly. A good physical with your doctor is a good place to start as many problems are found through examination.
Typical tests are a CBC which tells about your blood cells and platelets. This test will show if you have an infection, if you are anemic and several other things. Another basic test is what I know as a SMAC which is your blood chemistry and it shows if you kidneys are functioning normally, if your electrolytes are normal such as glucose, potassium and sodium. There is a lab test to show if you thyroid is functioning normally. Another important test is for your cholesterol which shows you total cholesterol, the good and bad cholesterol and your triglycerides. If any of the results are abnormal you will probably have more tests ordered. For instance, if your glucose is high they would do further testing to make sure you don't have diabetes. If your bad cholesterol is high you are more prone to have a heart attack or stroke. The doctor will encourage you to change your diet, exercise and he may put you on medication to lower it.
I wrote a hub about the DNA tests and if you have a lot of cancer in your family you might want to check into having those tests. They are expensive, I believe about $200 and insurance doesn't pay for them as far as I know. If you don't have cancer in your family they are not worth the money. There is not one test that I know of that will tell you what disease you are prone to get. Your family history is probably a good indicator as to what diseases might run in your family as some disease is genetic.
It is important to eat healthy, don't smoke, exercise regularly and if you drink alcohol do so moderately. Also, keep your stress level down as high stress negatively affects your health. I hope I have answered your question to some degree and I wish you the best of health.