[dugmartin]

You don't need to buy anything. Here is an excellent free open source AS3 (and other languages) editor/debugger (for Windows):

http://www.flashdevelop.org/

Download that and the free Flex SDK from Adobe, create a new Flex 4 project and stick this in the Application tag in the generated Main.mxml file and you are done:

    <s:Label text="Hello, world!" />

Use an AIR Flex 4 project instead with the same label control and now your app runs on both Macs and PCs (and Linux but not as cleanly) in its own native window with full access to the native file system and the Internet without any AJAX proxy issues.

I admit its not as nice as instant browser compilation but for some class of applications Flash/Flex is very nice.