Although I've never tried it, I've heard they have a decent fit in I Nuovi, which is more readily available in Canada and Asia than the US. You can buy their empty palettes through I Nuovi's website (http://www.inuovi.com), but after shipping and handling, I don't know if you'd save much money.
Other than that, I haven't heard of Stila's e/s and blushes fitting in any other brand's palettes.
I know, it gets me, too, that the empty palettes are so pricey. Some people just use empty pencil cases, etc, and use magnets or glue to make their own palettes. They're not as pretty, and the fit isn't as tight or secure, but they're much cheaper.