How much it costs to test a blood sample is going to very from jurisdiction to jurisdiction. I suggest you contact several labs in your area and ask for estimates.
But, why have the blood tested at all? Should not the State test the blood correctly the first time without you having to test it a second time? Maybe it makes more sense to put the State to its proof. Often times, a second blood test will just verify the results of the first blood test. Thus, you end up strengthening the case against you!
Further, beware: In WI, you must ask for the Department of Hygiene to preserve the blood sample in writing within 6 months of the date the blood is taken. You may need to do something similar in PA to have the blood preserved.
I strongly urge you to consult with a local, experienced DUI attorney. You can find such an attorney through the National College for DUI Defense: www.ncdd.com. Most inital consultations are free. So, you have nothing to lose!