Brum boss Alex McLeish would love to retain Manchester City stopper Hart, either on another season's loan or by signing him permanently.
However, Big Eck fears Hart will be out of his price range and is not sure City will allow the 23-year-old to be loaned out again.
Manchester United misfit Foster needs a fresh start, having failed to secure a first-team spot at Old Trafford.
At one stage, Foster, 27, was expected to go to the World Cup as one of England's three goalkeepers but has played so little football that it has become almost impossible for Three Lions coach Fabio Capello to pick him.
Meanwhile, Hart will find out today whether he is set for an early return to City for the season run-in. Birmingham are still considering a request from City to return the on-loan keeper after Eastlands No 1 Shay Given dislocated his shoulder.
But Brum want guaranteed compensation for any drop in league position as a result of Hart's unexpected exit.
McLeish's team currently lie ninth but could slip to 13th if they lose their final matches against Burnley and Bolton.
That could add up to £2.5m in merit money - and Birmingham are also due to pay City a £250,000 bonus after staying up.
Even a drop of two places would be worth £1.6m.
Vice-chairman Peter Pannu said: "We are negotiating.
"There is still a narrow gap there. Hopefully we can bridge that gap. If not, we will have to say, 'Sorry'. I'd like to help as much as I could without exposing my club."
City were yesterday given Premier League approval to move for Sunderland's Marton Fulop on loan.
go go go, go buy foster
ben is not as good as joe is.
see from the man city GK list
3 inj plus given
i think man city would wan Joe Back
but they gt fulop on loan =.=
foster is just an ordinary goalie. his kicking is lousy and his achilles heel is coming out to collect crosses. he is hopeless in that.
Just sell him. Get some cash for new players.
ya buy buy buffon, the best in the business or cech from chelsea.
Think Joe Hart is still better.
overrated
cause he is english.