this is for sa/ extra position, not a star.
For a star I would say
3 > 4 50
4 > 5 55-60
5 > 6 65-70
I don't like the idea of developing 3* unless he has 3 positions and a good sa.
Okay... It would be a lot of greens to pay, but he would also have really good skills right from the beginning. I think I will watch out for a 4 star 18 yo next season, this will be cheap and a good mix of both.
Will sell my FT in negos beginning of next season.