True. on line you can buy a new derailleur cheaper than just the cage probably but I'm sure you can buy cages online as you can buy them at your LBS. If you have an Ultegra derailleur, you can buy a used Tiagra or 105 for cheap and switch the cages. The cages don't wear out unless they are hitting the spokes, other than the jockey and tension wheels. I've switched cages but that was because I was given some by either I upgraded a friend's bike, he upgraded, the bike was trashed in an accident, I bought at a bike flea market.