Is the car disassembled? if so how much rust can you actually see/find? I took the whole car apart , put it on a rotisserie ,and had mine media blasted with Starbrite,safe effective cost about 5 to 700 bucks
If you go the chemical route remember you will have to neutralize the chemical after it is done,it will go in every crack and crevice.
Kind of a mess ,not my cuppa tea.
Then you can always grind it off, but then you risk removing steel.
so it can be done alot of ways ,just some of my experiences