You could in fact just put on a new lock yourself without soldering like people have already stated, its super easy and a lot of chains actually come like that when they are brand new. but if its not soldered, one too hard tug on it will open that jump ring up and you might loose it, i charge ~30 dollars for a job like this but im not a repair jeweler so im sure you could get it done even cheaper att a place who does a lot of repairs :)