GIMP is the best alternative to Photoshop, knowing how to use it, you could achieve similar results. There are many online Photoshop sites (they use a Ps script to emulate Ps) which work wonders also.
There really is no alternative. Yes, it is expensive but it is very worth it. It's an industry standard for a reason.
There many softwares which are alternative to Photoshop but the resources provided to Photoshop are much better than other softwares. GIMP is the best amongst others.
Artweaver and paint.net are easy to use, but they can't do as much stuff as Photoshop. Gimp can do a lot, but I think it's quite unintuitive to use. Another good one is pixlr, which is like an online stripped down version of Photoshop.
there is a free portable version of ps that is obviously reduced in functionality but ok for most simple edit jobs
No. Illustrator cant be a option for Photoshop. It is only for creating vector images like logos, illustrations, package designing. But Photoshop can do lot more than that. Illustrator's core purpose is creating vector images.
You can try Gimpshop or Gimphoto, they're modified GIMP so it looks similar to photoshop's interface and shortcuts. They're work fine on Windows and absolutely free. Thanks for the programmers. I like Gimphoto better than Gimpshop, but I like Photoshop better than them, heehe...
Gimp works well. Inkscape is good for vectoring; some prefer its trace tool to Illustrator's. Sumo.fi is so-so but can serve if you need a program you don't have to download.
I use ACD See Pro and LightRoom (which is a PhotoshopCS plugin but it can be used stand-alone). They are not free but u can find setup keys on the Internet, Google it
I have used GIMP. It is a lite and powerful tool. But the UI is a bit crappy at times. I have found some extreme flaws in their UI designs. But as a free tool, GIMP is a best alternative to PS. GIMPshop used to work earlier, but the thing is full of bugs as the developers are not updating it anymore. I would personally recommend GIMP.