I've been shooting sports for my college newspaper which has been great but I really need a 70(80)-200 2.8 lens to be able to cover indoor and night games. I'm working to put myself through college and I can't afford to drop $2500 on a lens. Should I go 3rd party? (Tamron or Sigma?) Is there a way to get cheaper used glass reliably? Do you know someone selling this lens?