I have done this job - $750 is well worth it depending on which coatings are being used. POR15 and Eastwoods Internal Frame Coat is what I used along with a test area that totally failed so now I have a quarter of the frame to re-do if not more.....
Saying "sorry" up front for this question...Is there any way I can flag this thread so when I go to a body shop and they want $2500 to just split the body off the frame?