There is no concept of uniform minimum wages across the entire country. Instead, each state decides on minimum wages, which are generally notified every 6 months. The notification is industry-wise and for each skill level.
However, since you are in Maharashtra, the salary of security guards will also be governed by the wage rates specified by the Guard Board Act. You cannot pay less than the rates specified by the Guard Board even if the minimum wage is lower.
Further, all statutory dues (PF, ESIC, cess to Guard Board) must be paid. You also need to provide for gratuity that would be payable after 5 years of work.
When deciding security guard charges paid to security contractors, generally amounts are added for uniform and shoes, which are to be provided free of cost to the security guards. Further, ensure you have factored in a reliever cost.
Please note that no security guard can be given a shift of more than 8 hours as per the law (12-hour shifts, though common, are illegal). One weekly off is required to be given for each security guard. If he works on the weekly off, then a compensatory off in addition to double-rate overtime is payable.