Luna is a terrible platform. It still has a large gravity well that requires massive amounts of fuel to land on, and return from. And the moon is a desert devoid of useful resources.
Building in low earth orbit will always be far cheaper.
It has a gravity well, but it is not accurate to call it 'large.' LEO is deeper into a gravity well than the surface of the Moon; it takes less delta-v to get just about anywhere (including Geosync orbit) from the surface of the moon than from an LEO on an inclination given by a launch from Kennedy Space Center.
Nope, it takes far more delta-v to get from Luna to anywhere because everything launched from Luna first has to be landed on Luna. Without aerobraking that takes a large amount of delta-v.
Building in low earth orbit will always be far cheaper.