'No cost' is probably a better phrase here. Especially because the word 'free' can mean:

1) no immediate monetary cost ($)

2)or shorthand for freedom, as in related to liberty. However,

"Generally, liberty is distinctly differentiated from freedom in that freedom is primarily, if not exclusively, the ability to do as one wills and what one has the power to do; whereas liberty concerns the absence of arbitrary restraints and takes into account the rights of all involved. As such, the exercise of liberty is subject to capability and limited by the rights of others."