Between 2008 and 2018 milk prices went down from $3.80 a gallon to $2.90 [1]. So we're actually barely above 2008 prices in non-inflation adjusted dollars.

To your specific point about targeting negative inflation, that's deflation, which most people believe is bad for the economy. Even if there are types of "good deflation", government policy inentionally targeting deflation would almost definitely be a bad thing.

1. https://www.usinflationcalculator.com/inflation/milk-prices-...