You can bake in the idea of a cash/equity split if the freelancer was interested as well.
The idea would be to limit projects based on time, scope, or budget from the get-go and stick to the MVP market niche.
Edit: Thinking about this idea more and reading more comments on this thread gave me another idea. Many people have commented that it might be a good idea to have your app fully wire-framed and thought out first. Need help with this specific stage before getting into the development of the MVP? Just another channel on the marketplace.
Idea Consulting -> Wire-frames -> MVP Development -> Design
All of course are optional and you could obviously swap Development and Design.