Howe is going through lists of potential targets with the club's recruitment team ahead of the summer window.
Newcastle have been linked with Olympique Lyonnais midfielder Lucas Paqueta – who is on Tyneside visiting close friend Bruno Guimaraes – but the 24-year-old could well be out of the club’s price range.
The 12th-placed club, which is 80%-owned by Saudi Arabia’s Public Investment Fund following a takeover late last year, must work within the Premier League’s Profit and Sustainability rules.
"Because of financial fair play, there has to be realistic expectations on what we can spend,” said Howe, United’s head coach.
“Our income, at the moment, as a football club, isn't as big as we want it to be in the future, so that impacts our ability to spend. For those people that think it's a vast sum of money, well, it's wrong.
“It doesn't mean we can't improve the squad, but it'll have to be bit by bit. It can't be an overnight thing, and that's due to the fact we need to expand revenue streams.”
Howe is ready to be “creative” in the transfer market. He said: “I’ve always had the mindset that you’ve got to be creative – and not moan or whinge at what you’re given. I’ve always had the mindest of getting the best out of what we have – and find a way to be successful with it."
United are 12th in the Premier League ahead of Sunday’s final game of the season at Burnley.