Maybe try a paint company"s wax and grease remover. Spray it on and let it sit and wipe it with a red scotch brite while its wet. A bit messy but it would be cheap!!
I spent about 2 full weekends using some "undercoating remover" spray-on product from Eastwood. I think I got more off due to elbow grease than anything. I finally torched and scraped it and that made the job much easier. What a PITA!!!! If I had it to do over again, I would have probably elected the acid bath.