You'd need a loan, and based on the current economic climate and the rate of failure in the food industry, no bank is going to give out a loan for somewhere that is based on a diet. Because even though it's not a 'diet' in the media sense of the word, that's still what Mr Bank-Man will see when he looks at your proposal and so it won't go through. The only way to make this work would be to open a place that serves great paleo food without making any fuss or deal about it, and building a following. That way it's just straight good food, no gimmick.