If you need the money, start integrating tasteful ads. Especially if ads are part of the intended eventual revenue model, getting them started early is more honest with your users, and starts your ad-optimization learning cycle. (In some cases, ads will even make a site look more professional/stable.)

If your userbase is such that it may react negatively, and you still need the money, consider a donation or subscription option. Or sell part of the venture, if the eventual upside can justify the trouble for you and risk for investors.