Hughton is looking to strengthen his squad at Carrow Road and has been linked with moves for Celtic striker Gary Hooper and Swansea forward Danny Graham.
"We are working hard but the majority of work is done in the last week or 10 days of the window," said Hughton.
"It's very difficult to bring in players at this time because prices are inflated.
"You have to make sure that any player you bring in isn't just an addition to the squad - they have to improve what you have got. We are working hard and we will continue to do so."
Hughton welcomed back captain Grant Holt in the goalless draw with Newcastle on Saturday, the striker coming on for the last 22 minutes after missing the previous three games with a hamstring injury.
"It was an important day for Grant. We weren't in a position to play him for 90 minutes," Hughton said.
"He will have another week's training and will be ready for next week."