From the Jan. 19, 1908 NYT we learn that football was king in Michigan even back then:

At the annual Michigan Athletic Association today it was shown that the total receipts of the last fiscal year were $33,894 [$776,000 in 2006 dollars]. Of this ammount, football brought in $25,894 [$580,000 in 2006 dollars and 76% of total revenue]. The baseball games lost $800 and track athletics $2,666. The management put $18,000 into the Ferry Field improvement fund and has a balance of $7,816. Last year the balance carried over was $10,545.

In 2006, football at the University of Michigan generated $50.982 million in revenues, approximately 83% of all athletics related revenue (Equity in Athletics data here).

We know that Michigan football is worth more today than one hundred years ago, but it is interesting to see that Michigan football is worth more today relative to the other sports on campus.