So it looks like the cost is about 21% (I know, weird number) of the total base value of the task. You still have to collect each individually, but you do get credit for your multiplier at the end, which is not shown in the value when you send them out.
Apparently, it will send out anyone who is currently available and has a task for that time in their current skin, as long as they don't already have a quest they are being asked to complete.
Edit: Ok, so the cost seems to depend on how many people you are sending on task. As I free up more people, the cost (as a % of reward) goes down a little. I'm sure someone will figure out the numbers soon.
Edit: Upon further investigation, I believe that the % cost is lower for premium characters(tasks?) than for regular tasks.