When I got photoshop I think it was a bit more than $150, and that was the student version. It’s not cheap. However, you can buy it pretty easily online and the earlier versions might be cheaper than the current one. I use photoshop 7 and refuse to upgrade; the interface is excellent.
As far as tablets go, they are good for some things, digital painting especially. Though if you are going to use photoshop for image editing/ matte paintings (like the signatures) it probably won’t help you much, if any. That’s just my two cents.