Photoshop is expensive. I think it retails for ~$800 to the masses, and $200 for the student edition. But Mac and Linux users have an alternative. Behold the alternative (yes, even on windows).
the GNU Image Manipulation Program
All the functionality of Photoshop, but free.
Note I said all the functionality. Not the power. One area where GIMP is lacking is a centralized distribution of actions (Photoshop will sell you packages of these), so you will need to use your interwebz research skillz to identify tutorials and scripts that fit your needs. Start with keywords "GIMP" and "actions". Also, many of the Photoshop tutorials are applicable.
Have you ever wanted to do stop-motion photography? I have. And here's my first one: