Coroplast signs are the least expensive material for a hard sign. Coroplast is often described as a plastic cardboard. These are often seen as yard signs or golf tournament tee sponsorships signs. They can also be used for larger signs if they will be mounted on a hard backing.
PVC signs give you a smoother look than the coroplast. PVC is not recommended for outdoor use, as the material can become brittle. It does work great for interior signage as it is 1/8" thick but still light weight.