If I had a nickel for every time that a minister or youth minister has said to me, "Well, I can't afford Photoshop," then I would have like, six dollars.
But seriously, there's a great Photoshop alternative for the Mac that's usually $50 that's on sale for $15. So go get it. Now.
In the Photoshop clones business, there's really only three alternatives: Pixelmator (Mac only), Gimp (Mac + PC), and Acorn (Mac). Acorn is a great Photoshop alternative that will let your edit and create images easily, and stop making your images look like junk on the web and in your Powerpoints.