I have a G5 and am running CS3. It has 2.5 GB of Ram and is the 2.7 GHz model. I run freak'n Photoshop on it all day. $200 or $300 would be a good buy.
However, here is my prediction. If you get it you will love it, and within a year you will be throwing other apps on it and wish for a faster and more powerful machine ^.X