What's the right price per course for adjunct faculty?

The SEIU says it's $15,000.
https://www.insidehighered.com/news/2015/02/09/union-sets-aspirational-goal-adjunct-pay

http://www.cengage.com/search/productOverview.do;jsessionid=271130676DA6A8B0075F6966BB787A19?N=16+4294922239+4294966221+61+4294949511&Ntk=P_EPI&Ntt=9344367867050971981083213667162986711&Ntx=mode%2Bmatchallpartial