50/50 especially does not work in that situation, where the split has been decided already by one side before any developer shows any interest.

Find a developer first who is interested. They'll tell you their motivation. Maybe they believe in the idea like crazy and want to build this. If so, maybe 50/50 could work. Maybe they are just looking for an item on their empty resume and can commit only about a month on this project. If so, 50/50 definitely is a recipe for disaster.

According to some people, if there is a tie, helps to have a veto power. 51-49 helps in that regard.