But do consider if you NEED to full version of PS CS,
Give PS Elements a look through. It might be just what you are looking for.
And much cheaper as well.
Even I, with 10 years of PS experience, dare not say that I use PS fully.
Download the trial version and see if it meets your requirements.
Actually, if you are not thinking of upgrading your software anytime soon, you can always get a student friend to buy an educational license. It's much cheaper than the full version.
Not very sure, but I think there's no option to upgrade to the next version when it comes along. The price difference is quite big, the educational version should be around $300+ only.