Yes, you should be spending over $100 on jeans. I picked up a pair of True Religions and a pair of 7s this weekend, both are great and will last years. I'm not typically a true religion fan because the pockets can look chick-ish, but if you get the right ones with the right fit and wash, they can be pretty solid casual jeans.
Yes, guys can wear pick, assuming they are the right guys.
Yes, Joe is spot on when he says being tan and in shape makes a big difference in terms of what you can wear and how you pull it off. Pitt can wear whatever the hell he wants and look good.
Finally, an Otis personal lesson -- I recently learned that fit is everything. You can spend $1k-$2k or more on an expensive designer suit, but if it doesn't fit right, it's wasted. Conversely, you can spend $200 on a suit from a discount center with a better fit for you, and you can look fantastic. Same carries over for lots of other clothes. So, for me, labels and price aren't what matter -- what really matters is the fit. As an aside, I'll notice the one place I really tend to stray on this is jeans. They're too much of a staple for me, the more expensive ones tend to fit way better, the fabric falls better, they look better, and they last longer.
The pages of GQ have some great lessons on how trim and well-fitting clothing can make all the difference.