The midfielder did spend time at Loftus Road last season, but was unable to prevent QPR from slipping out of the Premier League during a short-term loan spell.
Redknapp would welcome the opportunity to land the 22-year-old for a second time, but appreciates that Spurs would not let him go cheap.
With QPR now competing in the Championship, and having seen a number of big-money deals turn sour, they cannot afford to take financial risks.
Redknapp understands that and concedes that Townsend may be out of his reach.
He is quoted as saying by West London Sport: "I couldn't see us being able to buy him. I think Andros would be too expensive for us.
"Andros did great last season, but Tottenham don't want to sell him as far as I know."
Asked if it might be possible to put another loan agreement in place, Redknapp added: "I'd love to loan him, but whether they would do that I'm not sure."