If you decide to replace the crank set the crank set manufacturer will have a recommended BB to go with it - pretty straightforward.

I have a 2007 Roubaix and it has the Mega Exo crank and external bearing BB. I think it is an english threaded BB which means a simple removal/replacement using a few job-specific tools. Most threaded BB's are in the $20 to $30 range unless you want something super high-end.

Find the crank set you want first.