If you can figure out what the various milk subsidies and statutes all mean, you deserve a prize, but what matters to most Americans is that without the renewal of some price-support law within the next several days, a 1949 statute goes into effect that requires the federal government to buy up milk at twice the going price. That would mean payments to dairy farmers in excess of $7 per gallon, which would in turn drive up milk prices for consumers. (To get the farmers not to sell their stock to the government at $7 per gallon, consumers would have to be willing to offer at least that.)
For an overview of milk price supports, see this Mises Daily.