There is a .45 cent per one gallon tax credit for fuel blenders to blend ethanol with gasoline. There are no direct subsidies to farmer’s to grow corn for ethanol any more than there is to grow anything else. The reason corn gets planted and used for ethanol is do to the demand from the RFS.
Here a list of all the specific federal energy subsidies.
https://afdc.energy.gov/fuels/laws/ETH?state=US
Run what ever fuel your car likes. I have never seen a disadvantage to running 93 octane over 91 octane. If it is with in the budget, and can buy it local, i definitely suggest using 93. Should be no problem dropping back 91 if need be for part throttle cruising until you can get back to your local 93. IMHO. 93 straight gasoline is a better fuel than any of the lower octane fuel no matter what the mix. Especially for guys who’s car sits more than it gets driven.