Develop video casting solution for mobile / web app

I have a platform that has a web & mobile app where sellers need to run auctions live on video and registered viewers will bid live. The challenge we face is the number of sellers that can cast simultaneously (1,000+) with viewers for each around (200-300) which can reach 300-500K. And this is costing a lot specially with tools like AGORA which charge per min. If there is a way to have this solution in different model instate of charging per min, maybe charge per month reasonable amount.