On its own, a new PAC deal at current market rate would probably be worth about $400M/year or about $33M/year per school. But, you could maintain 85% of that value with the right 7 schools in a separate association....which increases the pro-rata share of those 7 schools to about $48M/school ($400M x 85% = $340M divided by 7 = $48M).
So, the B1G invites USC, UCLA, Stanford, Oregon, Washington and two others (likely two of Cal, Colorado, Arizona or Arizona State). Add the $10M value per school for the B1G Network's expansion into California and the West Coast and add a $10M per school premium - there's tremendous value to have the best PAC teams now associated with the B1G....and the result is a behemoth deal of $70M/year per school.