The pulleys are what needs replacement most frequently, being a wear item. If you do something to wreck the cage, which would probably involve a pretty good bashing, seems like it may mung up other things on the derailleur.
Anyhow, keep an eye out on ebay. Sometimes people just sweep out a bunch of parts, some half there, in a lot, sometimes half assembled, etc. Since this is a convenience mode for people, often the descriptions/pics are scanty, but you can get some pretty good stocks of spares this way.
These jumble lots tend to go rather cheaply.
Recently, I bought one lot that was 16 dollars plus 10 shipping. I got four complete Suntour Vx derailleurs out of this and spares for two more.
You might also figure out if the cage is used on another, cheaper model and pick up one of those.