At this point, no manager in their right mind would sign on - the Blades have had 10 management changes since 2007, and there's not even any proof that sacking a manager mid-season has any effect on performance. (interesting article on this, below)
They have money to invest. They need to buy (and it will cost them) a very experienced manager with contract stipulations that they will not be sacked for at least two years, regardless of team performance, and get this mess sorted out.
http://www.bbc.co.uk/news/magazine-23724517