It is dependent upon the type of toy cop car you wish to purchase. Hot Wheels has produced some small versions like you see at Wal-Mart for around a dollar. read more
or you could order from a parts store, the oe intermediate and tail pipe sections. when you get those, hang 'em, then measure where the muff would have gone and buy a section of pipe to go there. only price i can be in the ball park on is welds are usually ten bucks each. so depending on the config, that alone can be around 60-80 bucks. plus tubing and needed support clamps.. read more