Can you match the salary of your team member with what your well-funded competitor has offered him? Some people move for better pastures and, you cannot stop them. Change and moving on is a continuous journey of our life. We have build capitalism, our society on money and most follow it.
On the contrary, what you can do is provide a culture of love, empathy, creativity, fearlessness, and openness. And team members who believe in your journey and like these incentives and challenges will stay with you. These people will be the ones who will be an integral part of your organization, co-owners, and stakeholders. They might be perfect but no less than great humans and contributors in the journey.
Money is not the only thing in humans existence and living off well. Running a startup is challenging and is full of shock and paranoia. All we can do is minimize the risk of failures. We need a team of believers who lead from the front.