Militia is volunteers, not hirelings, so it is never appropriate to pay them, until and unless they are called up to continuous duty by State or federal government and in effect converted to a regular army.
Back in the Colonial period, government actually furnished rifles to those who could not afford their own. It used to be in many places, and was recently proposed by Dr. Ed Vieira, that a tax be levied on eligible persons who refused to serve in Militia, and the money used to compensate Militia members for their travel and ammo expenses or provided as a stipend for those purposes. This idea was unanimously rejected by a committee of militia leaders a couple of years ago. It was important to them to fund their own operations and be in no way dependent on or beholden to any level of government.
Internal finances of a Militia group will be no one’s affair but their own, They may want to raise money for hotdogs after meetings, or weaponry or anything in between. Whatever security they choose to provide or funds is also their affair. If they end up receiving funds from any level of government, then the funder may certainly require them to submit to an audit.
Liability concerns of leaders and trainers may make it seem desirable to incorporate. Handling significant sums of money may raise questions of tax liability, which can be diverted from the members by incorporation and minimized by pursuing nonprofit or charitable status. Whether any of this is worth the paperwork and scrutiny it will bring, I will not offer an opinion.