Streak today.

A project, A team and B team needs $2$ $\frac{2}{9}$ days to finish and they will cost $1800; B team and C team needs $3$ $\frac{3}{31}$ days to finish and costs $1520; A team and C team needs $2$ $\frac{2}{3}$ days to finish and will cost $1680. In under 7 days, which team is the cheapest to pick?