PVC is for making large runs (100,000 units etc). It is more expensive to set up because it requires injection molding which requires metal molds so the tooling csts are very high. The material itself is cheaper then resin especially if recycled PVC is used (the smelly one is recycled - McFarlane etc). PVC can tend to bend or warp over time under its own weight...
Resin is more expensive material wise compared to PVC (even though in Asia they use polyester resin and ceramic/marble powders to fill it plus they cast hollow parts) adn are done in much lower quantity. Resin won't warp under normal conditions (unless a lot of heat is present) but it can shatter if dropped.
