You can make a huge range of salaries. If you do car accidents, you probably won't make much money at all. If you do class action toxic torts (and you are good) you can be one of the most wealthy attorneys in the county. Think about getting a 1/3 contingency fee on a class action tobacco suit.
Isn't it a bit early to narrowing your focus?
Contact some attorneys in your area over winter break (after exams), preferably alums of your school, and try to do informational interviews with them about what it is like to practice law in this field - the upsides and downsides, etc. That's probably your best bet for finding information.
Do you guys have any ideas regarding how lucrative running your own PI firm would be though? That is the goal for me, not working at a PI firm. I am just going to work at a PI firm for a few years to figure out how the system works, and as soon as I have money built up and I feel I am ready, I am going to start it up.