Sorry to disagree. Still that is beyond legal authority of those handing out the grants. The large group of free market economists in Congress would be apoplectic if that were practiced. Right now a bill to authorize the USG to negotiate drug prices is being considered in Congress because the USG has no power to reduce the inflated prices that are charged in the US vis a vis overseas.
Finally there is money in the commercial markets that would be a lot easier and a lot less expensive. Also the. company could sell more shares to finance the trials. So saying that the company would forego future profits by selling the drug at 1/3 market prices to get some millions of grant dollars does not make sense.
I have had a GSA contracting warrant and a grant warrant. I have never seen your scenario. I would gladly applaud your research ability if you would document such an instance.