I think I've found a kind of a cheat in the game that will boost your wage budget, although I am not using it because it is unrealistic.
When you get an offer for an interview from another club and you accept it, usually your current club will offer you re-negotiating some things in order for you to stay at the club, especially if you are successful. Then ask the board for higher wage budget and they will normally accept it, especially if the club is rich. If you done really well with your club you will get a lot of interview offers and if you are using this every time you can get a lot of wage budget which you can then convert into transfer budget.
When you get an offer for an interview from another club and you accept it, usually your current club will offer you re-negotiating some things in order for you to stay at the club, especially if you are successful. Then ask the board for higher wage budget and they will normally accept it, especially if the club is rich. If you done really well with your club you will get a lot of interview offers and if you are using this every time you can get a lot of wage budget which you can then convert into transfer budget.