X2 I'm not sure media blasting of any type will effectively remove the undercoating. Might want to get some sort of agreement before work takes place limiting your out of pocket cost if it doesn't work.
I thinking soda blasting is more expensive than other media blasting. The one thing I like about it is it doesn't damage the metal as bad as sand does. The draw back to soda is it doesn't work as well on rusty metal. I have also read online there could be issues geting paint to stick after soda blasting, although I have never had any problems with misc small parts that I have done.