I have PSP 11 and I love it! I have a hard time with Photoshop and can't seem to get familiar with it. There is also another one called Photo Explosion that is fun to mess with. But if your heart is set on Photoshop someone ele might be able to tell you more about it.
I generally find my best deals by googling the software title and looking that way. Sometimes you can get lucky and Bizrate, or Pricegrabber or nextag. Most of the time my best deals come from Amazon.com.
Also, google "coupon codes" for money off coupons. Something like "Amazon coupon codes" or "Photoshop coupon codes" maybe even try "Photoshop rebates"
Good Luck!