Everything belongs to God and we can't give it all for free!
Yes, technically everything does belong to God, even our very lives. So it could be argued that we must give everything we have for free without exception. This would be like treating the early disciples' communal ownership of property as prescriptive rather than descriptive.
The multitude of believers was one in heart and soul. No one claimed that any of his possessions was his own, but they shared everything they owned.
It is not argued that everything must be freely given, but it is argued that all ministry should be freely given. There is an important distinction as ministry is to do with that which is spiritual.
The scope of Jesus' command
Interpreting it too broadly or too narrowly misunderstands Jesus' expectation for ministry.