How about reaching out to companies for sponsorship?
Companies like Amazon, Google, Mercado Libre (South America), BT (British Telecom), Tesco, Argos, Sony, Nintendo, TIM (Italy), Pirelli and much others could be potential sponsors.
These sponsors could have their advertisements displayed when managers log in or through other preferred methods.
The sponsorship money received by iGP would be converted into tokens as championship prizes:
1st place: 180 tokens
2nd place: 85 tokens
3rd place: 40 tokens
All other participants: 6 tokens each
*Valid only for Leagues with the maximum races possible per season (Or, if there are fewer races, the prizes should be proportional, with a maximum of 180 tokens per month.)
** Improvements for this idea is highly recommended
*** I think it's a win/win/win (iGP, managers and sponsors)