The price difference between a sheet of true 4'x8' coroplast and a sheet of 1-sided MaxMetal is $34. The cost of vinyl, printing, and laminate is the same no matter what substrate you use. Your sign uses two panels. Therefore you are wasting your time asking a really stupid question over a $68 difference in price for the sign that is the visual calling card of your business. Coroplast, no matter what anybody says, is not a material that should ever be used for a permanent site sign for a business. Even if it manages to survive the UV light somehow, it will never stay flat, it is not dimensionally stable, and you will always have a ridged surface to look at and the ugly corrugated edges. A Coroplast sign used in place of a proper substrate for a business's sign tells the customer that the business is not planned to survive and is not to be trusted. It also tells the potential customer that the business will cut corners and not deliver the best product to them. The same is true of using a banner instead of a sign as the main business sign. When either is used as a sign company's main sign, it tells the potential customer that this sign company does not know what it's doing with signs, and cannot be trusted as a resource for giving them the best sign for their money.
Make new faces out of ACM and put them up. Throw the old ones away (or put new prints on the back of the old faces if the material is two-sided and in good shape)