Make sure you ask for Lexan material for the surface. They made me some decals laminated with matte vinyl, and it's way too soft.
You can prolly clean your current sigsn really good, then put these lexan overlays right on top.
Where do you get your signs? Even VisitaPrint costs $50 for such a simple 12"x12" metal sign.
I think that Kleen-Rite has some decent looking signs. I'm not sure what they make them out of but I've heard great things about Kleen-Rite.
"Dirt cheap" is the only good thing I hear about Kleen-Rite.