What does outlast do?
You do not pay the cost twice. The part in parentheses is called reminder text, and doesn't actually do anything it just reminds you how Outlast works. The card would function exactly the same if it read "Outlast {1}{B}"


  207.2a Reminder text is italicized text within parentheses that summarizes a rule that applies to that card. It usually appears on the same line as the ability it’s relevant to, but it may appear on its own line if it applies to an aspect of the card other than an ability.  
  
  702.106. Outlast
  
  702.106a Outlast is an activated ability. “Outlast [cost]” means “[Cost], {T}: Put a +1/+1 counter on this creature. Activate this ability only any time you could cast a sorcery.”