I think the list of equal or better alternatives are slim.
Shane Battier
Josh Howard
Grant Hill
Tayshuan Prince
Luc Richard Mbah a Moute
Andrei Kirilenko
Thadeus Young
All these players are available and though I am sure the Celtics can't afford a few, they could afford a couple at much less than what they would have to pay Green.
Which couple do you think would be significantly cheaper: Luc Richard, and Mbah a Moute?
I am guessing these price ranges ...
Jeff Green = $35 million, five years
Shane Battier = $20 million, four years
Josh Howard = $8 million, two years or $9mil, three years or $5 million, one year
Grant Hill = $3 million per annum, one or two years
Tayshuan Prince = $26-28 million, four years
Luc Richard Mbah a Moute = $11 million, four years
Andrei Kirilenko = $25 million, three years
Thadeus Young = $335 million, five years