Assuming a regular 5x5 league, you should do that without question. Rollins is proven and a 1st-2nd round pick (and probably the 3rd best SS fantasy-wise), Pena is good only for power, and you can probably find a host of similar guys on FA (eg - Burrell, Thome, Giambi, etc), and Bonafacio, while he may end up having an amazing year, is still an unknown quantity. Plus you gain a roster spot, which is almost always useful. Your biggest worry is that it might get vetoed for not paying enough for Rollins. Worst case scenario (barring injuries or Rollins somehow imploding) is that it is a wash. Best case scenario is that Bonafacio cools off and you got rid of an undrafted prospect for someoen's 1st or 2nd draft pick.