I think the cheapest and fastest way is direct contacts with investors. If you have a good product, of course.

You have 3 options:
1. Hire a cool team and spend $ 300,000+ on marketing.
2. Use the Investor databases and contact investors directly.
3. Hire an army of bounty hunters.

Offtop: Maybe for you will be useful Ultimate ICO Starter. This is a free document for the creators of ICO.