The Shakers are due for a windfall of around £1.25m following Nugent's switch from Preston to Fratton Park.
However, Casper will be expected to wheel and deal at the bottom end of the transfer market as the directors look to invest the cash boost throughout the club.
Harrop told M.E.N. Sport: "There is no way the directors will be handing Chris or director of football Keith Alexander an open cheque book.
"That's not going to happen. The windfall will be used to benefit the club as a whole."
Harrop wouldn't confirm the exact amount Bury can expect. But we understand a 20 percent sell-on clause was written into the deal that took the England international to North End in 2005 for just £100,000.
"It will be a substantial amount of money," he admitted. "But the payments we will receive will be structured in line with David's four-year contract at Portsmouth.
"The budget for players has already been set this season. And any money received will go on all areas.
"We want to invest in the youth system to try and find the next David Nugent and we want Bury to be as attractive as possible to youngsters.
"We're also looking to pay off our mortgage so we actually own our own ground rather than a third party."
Casper will have a number of potential new faces on view against a strong Everton side at Gigg Lane on Saturday.
Much travelled Drewe Broughton, Accrington's Andy Mangan and Hartlepool keeper Jim Provett can all clinch deals with good performances.
However, there's no place for last season's leading scorer Andy Bishop, currently suffering with tendonitis.
"He will be fit for the start of the season," insisted Casper. "It would be great to have some money to spend but that's not down to me. Hopefully, they can find some to spare."
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