Leeds are expected to lighten their wage bill by selling Mark Viduka, while Dominic Matteo and Michael Duberry are also attracting interest.
Jason Wilcox, Michael Bridges and David Batty are all out of contract next month, which will reduce the wage bill even further.
Blackwell wants to start his rebuilding programme and hopes to bring in a lot of new faces.
Blackwell added: "If some of the players that we think are going do not go, then that number will be reduced but it will still leave us having to get 12 or 14 in."