Other then two queries one for paid and on for free or creating a custom SQL query, its not possible natively.
That’s not what taxonomies are for. Taxonomies are for grouping, not
for ordering by. If you want to order by something, it has to be
something in the post itself, not a term in a taxo. Otto
So It would make more sense to set the Paid / Free as post meta and the sort by it.