Town have made six signings so far in the summer transfer window – including bringing Matthew Pennington and David Davis back to the club – but Cotterill still has a series of targets on his radar with the squad requiring work.
The Shrews chief conceded he has found the window 'very, very difficult' to work in and the situation of additions arriving towards the end of pre-season is not ideal.
As it stands Town only have one more friendly – away at Exeter on July 31 – lined up after tonight's short trip to Hereford. Shrews face the added complication of key men Aaron Pierre and Ollie Norburn being away in the United States, competing in the Gold Cup for Grenada.
Cotterill said: "Ideally you'd want everybody in by July 1 so they start the pre-season and end up doing the work all the others have done.
"We haven't quite been able to manage that.
Trying to get everybody in is very, very difficult at the moment."
Pennington, Davis, Elliott Bennett and Luke Leahy checked into Montgomery Waters Meadow on free transfers and the club parted with fees to bring in Ryan Bowman from Exeter and Marko Marosi from Coventry.
"There are free transfers out there which you try to attack first, once you attack those – or nominal fees – where can you go then?" Cotterill said.
"Then you're in the market of 'is there any money to buy anyone?' then you're in for loans or people still left out there.
"Sometimes they are still out there because maybe they want too much money and we can't afford to do that.
"We still have money available to us but we have to make sure we not only spend that on the right players, but spend it wisely."
Goalkeeper Marosi is set to be available to make his first Town appearance tonight after missing the friendly at AFC Telford last week.
Meanwhile, Peterborough director of football Barry Fry has insisted that Shrews left-back Nathanael Ogbeta is 'no longer a target' after Posh previously tried to sign the 20-year-old starlet.