This is the most common problem I deal with as in our Mentors 2 inventors group. Inventors are notorious for spending too much time and money on prototypes and product and not enough on business or marketing. In my experience launching over 250 products, zero budget is not going to get you anywhere. Small budgets don't work either. Speed to market is essential. My suggestion is partnership. Find partners who will market for you. Be prepared to give them a very large cut! Remember that a product is nothing if no one buys it. The power is not in PD and invention but in who has access to the market.