Is it permissible to repay a wheat debt with a sum of money agreed upon based on the prevailing prices at the time of the contract and previous years, despite the current high prices?

It is not permissible for the questioner to give the debtor the value of the wheat owed, because this falls under selling food before taking possession of it, which is the view of the majority of jurists. As for the Malikis, they permit selling a commodity that has been delivered through a salam contract before taking possession of it, to the one who owes it, provided it is not food. The high price at the time of maturity does not affect the obligation to acquire the commodity delivered through the salam contract.