Most of the tracks dropped about 30-40%. Those 24 hour races went up a lot, and a few outliers were dropped 50% or more.There was 2 races with increased rewards as they gave almost nothing before.
There was 16 races with rewards slashed by 30-60%
Most were 30-40%. Doing reverse math, it basically means playing those events, you'll have to play them 50% more to get the same amount.
For example, any that went from 35,000 to 25,000, you could play it twice before (get 70,000), but now to get the same money you got to play it three times (get 75,000).