Doncaster have made forward Dany N'Guessan their sixth summer signing.
Tottenham have confirmed that Romanian defender Vlad Chiriches has completed a move to Napoli.
Bruce has already spent £15million on the capture of midfielders Robert Snodgrass and Jake Livermore, with a fee still to be decided by tribunal for winger Tom Ince.
But Bruce, who brought in Curtis Davies and Tom Huddlestone for relatively modest fees last summer, said he did not yet have the scouting network overseas to feel confident in signing more foreign players.
"There's the problem in our game. You identify a young English lad but you can get a player from overseas for half the price," said Bruce.
"If I can buy in our market I always will. You pay a premium for a young British player and that's what we've done.
"We've got a 22-year-old, a 24-year-old and a 26-year-old. It's cost us more money but I would expect that.
"You know what you're going to get. There'll come a time when I know what I'm going to get from the foreign market and hopefully we can get that set-up in the next 12 months."
Meanwhile, Bruce admitted talks to sign Tottenham centre-back Michael Dawson are "at a stalemate".
Bruce led Hull to Premier League safety and a place in the FA Cup final last season, an achievement which earned them a place in the qualifying competition for the Europa League.