When and how much?
The Triumph is $300 or less in stores. It is available now.
Will it only be on the $60/month plan?
After Virgin Mobile switched its plans, new users can only sign up on the old plans: $35, 45, and 55 respectively for 300, 1200 and unlimited talk (and unlimited text and data for all.)
Old users can grandfather their existing VM plans.
Where can I find the specs?
Here for starters.