Based on news reports from the archives of the Fort Worth Star Telegram...
The growth rate for the prices from 1991 to 2010, when prices basically levelled off, was 10.8%.
I couldn't find a price for the 2004 grand champion.
The 1996 grand champion only got $100k because it was the 100th anniversary of the show.
That big dip below $150,000 was in 2009, the February after the 2008 financial crisis stuff hit the fan.
Based on normal inflation, the 2016 sale price of $210,000 is still five times what it was in 1991.