This is an interesting idea.

why can't someone pay for an academic collaborator? In other walks of life, we often pay for crucial knowledge in a field we don't have expertise in. In the consulting world, research reports are routinely written with individuals who have been paid for their services. It seems that pay for collaboration should be prohibited only when it threatens the integrity of the work. For example, it should be prohibited when the work has already been produced and wealthy individuals are seeking only to attach their name to scientific work in an attempt to buy prestige. This seems to have been the case for the calculus theorem known as L'Hopital's rule, which some believe to have been discovered by Johann Bernoulli, who might have been paid by the wealthy aristocrat Guillaume de L'Hopital ...

But if there is no conflict of interest, or damage to the integrity of the work, then it might be worth considering. It is often common for a researcher to realize they have no knowledge in an area which is crucial to completing their research. One option is to completely master a new field. Another is to hope that a specialist in that area will collaborate out of the goodness of their heart. While these are desirable and preferable outcomes, they are also difficult to obtain. It might also be useful to simply hire someone to help solve a particular problem. As long as the payment is acknowledged at the beginning of a scientific paper ("Professor X has been compensated for his assistance in this work..."), collaboration for pay might be a form of scientific cooperation worth considering.

From Fabio Rojas, regarding the Tozier story that Erin O'Connor also covers. Tozier responds in Erin's comments section.