Leaf springs are made from 5160 steel. Beyond that you get what you pay for. Having a set of existing springs re-arched is another case of getting what you pay for. A properly re-cambered leaf spring should give the same service life as it did originally. It's not unreasonable to spend the cost of new springs to have a set of factory springs rebuilt correctly, if not more. You get what you pay for. Cheap replacement springs are usually just that.
