The reality is that you can't train all your players in this game. The plan should be to one or two position train and sell some of the trained players to get enough money to buy good quality players in the positions you're not training.
re: Extreme salaries
It's important to remember that salary increases are not linear, so the difference between the cost of respectable to strong jump shot, and the difference cost difference between prolific and sensational are not even close. It takes a lot of pops to get a player from $5000 to $15000, but it takes a lot less to get a player from $20000 to $30000.