"Five years ago we could sign players for 40 or 50 per cent less than they were on and take them for nothing.
"Now if they are any good it's a £4million fee and another £2m in his contract. Good players know what they are worth and if you don't give them it somebody else will.
"If I had spent £40m I could have got fourth," he said. "£30m would let you finish sixth now, or even seventh. The spending equates to points gained.
"We have created a level in our own squad and if we want to go out there to increase it we will have to pay more for it. It's a difficulty for a number of Premiership clubs - not just ourselves."
Meanwhile, Bolton are reportedly tracking Real Zaragoza's prolific striker Diego Milito, Espanyol's attacking midfielder Ivan De La Pena and fellow Espanyol defender Alberto Lopo.