The bad thing about blasting is that you will have sand everywhere. Isn't cheap either. Google sabdblasting in your area and see if you have someone local around to do it. Might save you money and usually they are experienced. You can block the areas that shouldn't get hit. If you have the outer skin showing from the inside, they really shouldn't hit that area to hard as you can see what happened to that guy on that site that was listed. I take the big parts to a guy in our area because of the cost and mess. Especially the mess. You can always cut out the bad spots after it's blasted. Good luck.