paint my front 2 side doors and boot

[cfoo1]

Hi, I plan to paint my 2 side front doors and boot due to scratches. However, when I check 2 differrent shop, their price range fr Rm400 to RM800. What a big different, which make me worry. Really don't know which one give the best quality. Any recommendation how to chk whether their paint is good or not good? How many layer of paint they shd use?appreciate your comment