Flash through Flex

Flash is expensive.

We all know this fact, and the current version falls in at just around $700. That's a steep price for a product that you're just learning. There are lots of options though.

You can buy on the cheap. Doing a little searching around you can easily find a copy 1-version older of Flash for quite a bit cheaper ($300-$400).
If you're a student, the student discount will get you a copy even cheaper than that.

If you don't need flash for animation, but instead are interested in it for programming, an excellent alternative is Adobe Flex. Flex uses the same Actionscript 3 libraries as Flash does. Flex applications can be written entirely in Actionscript 3. Hard to believe I know, but checkout this tutorial.

This isn't new knowledge to the flash development world, but if you're looking to get your Actionscript hands dirty, or if you need to spend some time with AS3 and don't have Flash to mess around with, shoot for Flex SDK, you can do more than you think with it.