Marriage in Judaism is technically a purchase of a woman with at least two witnesses. So, I was wondering if it's technically possible for man A to negotiate the purchase of the wife of man B (to then directly become the wife of man A).
The short answer is no the only way a married woman can marry someone else, is by first receiving a get from the first husband, or after the death of her husband. (Rambam Hilchot Ishus 1:3)
And as soon as she receives the get she is free to do as she pleases, so if the first husband made a deal with someone else, she is not bound to follow it. And if the husband gives her a get and tell her that she's divorced as long as she marries B, that's not a valid divorce (Rambam Gerushin perek 8)