Manchester United have struggled to maintain their dominance this season following Ronaldo's £80 million move to Real Madrid in the summer, and Ferguson has always insisted the funds from that sale are still available.
However, he insists it is not his way to spend £60 million on a player and says there is no chance he would offer a similar fee for anyone except Ronaldo.
Asked if he would pay that amount for Lionel Messi, he said: "No. I'd pay £60 million to take Cristiano Ronaldo back but that's about it.
"The market is inflated. Agents get in touch with our chief scout and say this player will take a drop in wages from £10 million to £8 million. And it's only £42 million now. So work it out.
"You bring in a player for a £40-odd million fee, then you take in their salary, with the euro against the pound, and the tax rate here, so with a five-year contract and wages they're talking about £8 million a year. So instead of £42 million, it's £82 million."
Ferguson again dismissed the suggestion his approach to the market has been influenced by the club's owners.
"The proof of the pudding is the eating, isn't it? They've given me £20m for three players already and any time we've asked - for Dimitar Berbatov for example - they've done it, they've supported it."