Wouldn't say no to Broadfoot but I imagine he would be on a decent wage. Certainly wouldn't be worth breaking the wage structure for.
Riordan, whilst good on his day, is not worth the trouble.
Kerr is probably the best shout of the three mentioned. Nothing outstanding but a good professional with experience in the league. Wouldn't be asking for too much in the way of wages and could do a job in the same way that Clancy did last season.
As others have said though, I would not be surprised if we end up with someone none of us have head of; either a loan signing for cover or someone with a tenuous link to Bradford...