Looking outside the well known Graphix apps has anyone had a play with Photofiltre ? It is reputedly very powerful and well featured but also free. I used it a few years ago and it had all the capabilities of Photoshop at the time. Find it on www.snapfiles.com in the Free Section under the Graphics and Photo Heading, Image processing.
You mentioned yr two sons. Why not just buy a student version of PS for $179. That's what I just did, and for the learning curve, I've ordered a book from amazon for $50. That way, you can have the industry standard at a reasonable price.