Earlier this year the Black Cats' 10-year tenure in the Premier League came to an end following a disastrous season that saw them pick up just six wins from their 38 games.
Off the field, the club has run up debts in excess of £100m and American owner Ellis Short has refused to provide additional funding as he looks to sell it on.
"The income drop after relegation, from £100m to around £40m, has to be considered and so does the wage bill, which is still significant for this level, even though we have taken steps to reduce it," Bain explained in an interview with the Sunderland Echo.
"We've brought in £30m for Jordan Pickford, but that is needed for the running of the club. Yes, that money comes in, but then you have to consider the money that went out on legacy transfer payments at the start of the summer.
"I'm sure that Ellis looks at the football club now and recognises that he's made mistakes. He spent an awful lot and now wants to do things differently.
"We have to do things in a way where we can get steady growth and be more sustainable, so that we're not being knee-jerk in what we do. We couldn't continue the way things have been in recent years but he is absolutely, categorically still funding the club."
Sunderland have had a tough start to life in the Championship under new manager Simon Grayson and currently sit one place above the relegation zone, having taken just six points from their opening eight games.