Spurs are looking to replace playmaker Luka Modric, who is likely to join Real Madrid later this month, but Moutinho is not an option despite having worked under Villas-Boas at Porto.
"The level of expectation of Porto over [the price] is difficult," Villas-Boas told reporters at the Tottenham training ground ahead of Saturday's league opener at Newcastle United.
"Porto sell expensive but they sell a good product. They have pride in defending that kind of ground."
Asked if Spurs would be able to sign Moutinho, Villas-Boas added: "No I think it's very difficult."
He also ruled out a move for Stade Rennes midfielder Yann M'Vila although Spurs had considered the France international.
"He's an interesting player but I don't think he'll join Tottenham," said the Portuguese.
"He's a defensive [midfield] player. For a possible solution for Luka we're looking for a more creative player. We had initial interest in the player but we have moved on from that."
British media reported Spurs were close to agreeing a deal of just over 30 million pounds to sell Croatia midfielder Modric to Madrid and Villas-Boas said he expected the clubs to finalise the transfer before the window closes.
MODRIC DEAL
"I think we will have a conclusion in the next couple of weeks," he told reporters. "From what the chairman [Daniel Levy] has told me talks are ongoing.
"Negotiations that stalled at the beginning are now back on track and reveal our willingness to try to find a solution.
"The targets [to replace Modric] are identified, it's just a question of how quickly we can close the deals," he added.
"It will be dramatic for the club if we cannot find the right replacement but we are looking to strengthen the squad immediately if eventually the transfer goes through."
Villas-Boas, 34, also said he would make gradual changes at Tottenham in contrast to his attempts to quickly overhaul an ageing squad at Chelsea which eventually led to his sacking.
"There are changes which have to be made but I think that I won't promote that change as quickly as I did at Chelsea," said Villas-Boas, who has replaced the sacked Harry Redknapp.
"When things were going smoothly everybody is happy and you're able to progress it. When you are faced with a setback, it's your ability to bounce back... that will keep you on track.
"At Chelsea three defeats in a row last year had a tremendous impact and when we wanted to correct things, we were always putting the fire out and never establishing what we were before.
"I think it's best to go for a gradual change. You have to respect what has been built here by Harry and hopefully I can do exactly that."
