I push back on the premise of the question.

Before you look to find a co-founder or spend a cent on building something, make sure you've thought your idea through. Who are you for? What's the problem you solve? Are you clear on the insight you are working against and the positioning you will use when you bring the product to market? Many of the problems I end up working with founding teams on down the road can actually be traced to them having started out building something and then trying to figure out how to sell it, rather than starting with the need and a clear view of their prospective customer.

Spend your time and money there, first.