Derek McInnes would like "one more" new arrival before the transfer window shuts on Monday night but admits Hearts are "up against it" with clubs raising prices.
The Premiership leaders have already landed permanent deals for right-back Jordi Altena, winger Islam Chesnokov and a loan for midfielder Marc Leonard.
They've also fast-tracked a deal for striker Rogers Mato, who was due to join on a free transfer in the summer, to get him to Edinburgh this month.
But head coach McInnes admits the £10m investment last summer from Brighton owner Tony Bloom, whose Jamestown Analytics company is used for Hearts recruitment, is presenting some problems.
"We'd still like to do one more," the Hearts boss told Sky Sports about potential new arrivals.
"The difficulty we're finding, because of our position in the league and because clubs are now aware of Tony Bloom, everybody thinks we're awash with money, which we aren't.
"Sometimes players we've maybe identified can soon become outwith our reach because clubs start to raise the fee and raise wages so we're up against it a bit.
"We'd like to bring in one more if we can but if we don't, if the window shuts with what we've got in the building, I'm confident we can make a right fist of it."
Hearts are four points clear of Rangers and six clear of Celtic and have only lost two league matches all season.
McInnes has reportedly attracted interest from Leicester City after they sacked boss Marti Cifuentes this week.
But the former Kilmarnock manager stressed his commitment to Hearts.
"I don't know where that's come from," he added.
"These things you just take with a pinch of salt really. I think it's clear my focus is here and I'm in the job that I want.
"I think there's work to be done here and I just want to make sure we finish the season as strongly as we can."
