Chlorine is by far the least expensive of the halogens as it is derived from simple electrolysis of salt water. Polyvinylidene fluoride is used commercially but it is much more expensive than PVC. Bromine and Iodine are much more expensive halogens and more labile. That is, the resulting vinyl bromide and vinyl iodide are susceptible to reaction with nucleophiles (bases). PVC is cheap, stable and easily moulded into solid parts (like plumbing pipe) and easily plasticized into "vinyl" for car interiors and furniture.