I really can not imagine that you would need more than infranview, gimp or Picassa for pen photos utilization. I own and operate a Photographic studio, and we specialize in sports "team" photos....we still do weddings and seniors and so on, but we make the bulk of our living on sports teams. Some of the leagues in this area are huge. 200, 600, even 1200 kids in a league. All in all we photograph around 20,000 kids a year. Needless to say we spend a fair amount of time on computers. We generally use production software to convert our files and do some minor corrections. Any correction that is more than a click or two we use PS CS4. I have it on all our computers. It is very expensive, and as was mentioned very deep. I have two people that all they do is graphics, and they along with me may use 15% of the programs capabilities. They may only know 20% of it's abilites total. It is a very deep program. We go to seminars and always come away with new methods, shortcuts and even new looks for the end product. It always amazes me that these "new" methods have been in that program all along.
PS is very expensive although you may note that there are many different prices in the overall pricing structure. Not having bought PS lately I think the full blown current version is about 700 to 800.00. You may see the "student or educator" version for 250 to 300.00 These are full and complete working versions, however are not upgradeable. In other words when the new upgrades come out they are not capapble of being upgraded at all. The upgrades are usually 150.00 or so.
What I may recommend is to buy a full blown- out of date version. Sometimes software vendors have them for 350.00 and up. They may be two or three versions ago, but these are certainly viable and working versions. Plus you can upgrade for 150.00 if you so choose. I would not go any further back than CS2. This, (I believe) is the version that introduced "PS bridge" which is a great library program. Upgrades will update your program to the current version, even if you are two or three versions back.
Do not discount these free versions on the internet...Infranview, gimp etc...they have tons of capablities, and are really rather well done. It just depends and how involved you want to get.....but make no mistake, Photoshop is the granddaddy of them all. It all depends on how deep your pockets are and how much of an interest you have.
Also Light room is a production software, in other words it is made to do the same command to multiple photographs. We use it some, but I am not sure I wil ever upgrade to other versions, as it does not seem to be all that needed.
Moke