Even without modding the Powershot is a great camera series. I have installed CHDK on my Powershot memory card, and I would highly recommend it.
With it installed I have access to RAW images, made a working shutter release for better control, and can run scripts to automate the camera such as the macro focus stacking. CHDK allows the camera to set hundreds of options, many only available on the top of the line series cameras (or many not even then). Heck, it even puts Tetris and such on there for fun.
Just get the best model you can and go from there. If you have any questions about it all feel free to PM me, I've helped others with it all before.