Something I posted on another forum...

In MotoGP the host pay's a flat fee to Dorna, usually around £3m I believe. The local government usually supports the host company as they are bringing in visitors and revenue.
The host works purely for the gate money, event sponsors money, stall and exhibition holders payments, programme sales plus any assistance in revenue from the government. From this they must staff the gate and look after the policing etc., plus pay for the hire of the circuit.
Dorna gets the TV rights, the host's fee and sponsorship money from series sponsors. They also take a series entry fee from each competing team.
In return, they bring a circus to town, completely organised and ready to go. They subsidise travel and help to fund teams including some of the lesser teams in return for a say in how these teams are run. They also subsidise travel costs etc.

MotoGP is struggling at this time, sponsors are thin on the ground and costs to teams are under scrutiny and pressure. This is why Dorna settled for a £4.5m deal to allow BT Sport to have sole rights to live TV coverage in the UK. This despite the serious lack of exposure this has caused, they needed the money. The last GP of the year had UK live viewing figures of 125,000 compared to 1,200,000 for the same event last year.

Substitute IOMG for Dorna and you get an idea of what they could be up against if they get it wrong. I think they should look at this and it has its merits, but I am in two minds as to whether they can make it work or not.
Being a road circuit, I imagine that the 'hire' cost would be less than a full motorsport complex and being a lesser championship than MotoGP, some of the costs will be an awful lot less all round. For example, machinery costs are a fraction of those in MotoGP and rider/team salaries much the same. As already mentioned, a lot depends on sponsors realising the value in the series.