In lease based contracts, such as Ijarah and Diminishing Musharakah, the rental indices can capture the true essence of pricing as per the nature of transaction.
Using Rental Index in Fixed Assets Finance
Output Price Index as a Pricing Alternative in Islamic Finance
Repo transactions are not compliant with Islamic principles due to the buyback nature of transaction plus the use of interest based securities as underlying assets. However, in commercial contracts where Islamic banks would like to earn return, there is need for a pricing benchmark to mitigate risk as well as ensure transparency in the contract.
Islamic Economics Project 