In 2016, a South Dakota initiative to set up a top-two system, without any party labels, was on the ballot.  It received 44.5% of the vote.  Proponents of the 2016 initiative spent approximately $1,600,000, whereas opponents spent $300,000.

The proponents are trying again, although this time their initiative leaves party labels on the ballot.  The same New York-based organization Open Primaries, which had contributed $1,356,720 in 2016, has just forwarded $140,000 to pay circulators to get the new initiative on the ballot.  See this story.

Open Primaries gets most of its money from the John and Laura Arnold Foundation, which is based in Houston, Texas.