Wordpress has a quite a few free good looking themes on their website - wordpress.org.
So there's no need to buy someone's theme unless it is 100% the layout and can do what you want to do on your website.
If you don't want to use a default theme from wordpress, and are one of Marcus students, he has several theme you can use for free. However I prefer creating my own themes using Artisteer. Artisteer is only around 60 or so dollars. With Artisteer, the sky is the limit with what you can do with it.
You can create your theme headers in any graphics program. I use Gimp, it is free and is a slightly lighter version of photoshop. Unless you are a digital professional artist, there is no reason to have photoshop. just go download Gip. - yes their is a learning curve as with any good powerful program.
Another program I use heavily is Snagit by Techsmith. It to cost around $60 but is will worth it. For most of the stuff you will be doing, Snigit is fine and has a low learning curve. This is also you see Marcus use a lot in his webinars.