I hired a Canon 70-200 f2.8 II for 11 days earlier this month and it was £170 all in.
That would still be too expensive for me considering it's purchase price is only £1,320. It seems that it's just not feasible to offer lens rental at low enough prices, if it's equipment you anticipate needing on even only a few occasions it seems better to buy. Especially considering you can sell the lens for practically the same price you bought it at, whereas rental is money gone for good.