Spaceplan
I love it! Found myself doing mental calculations for the most effective thing to buy next, and the next thing I knew I'd written a script to automatically buy it:    var clickBestThing = function(){
       var things = [...document.querySelectorAll("#manufacture__container > div")].map(function(e){
        var res = {e};
        [...e.getElementsByTagName("span")].map(function(s){
          res[s.id] = +s.innerText.replace(/[^0-9]/g, '')
        })
        if(e.id === "item__spudGun" || e.id === "item__potatoLauncher") res.powerGain *= 1000;
        res.score = res.cost / res.powerGain;
        // res.score = res.cost / res.spudGain;
        res.name = e.getElementsByClassName("manufacture__name")[0].innerText;
        return res
      }).sort(function(a,b){return a.score - b.score})

      window.things = things;

      var bestThing = things[0];
      if(!things[things.length-1].score) bestThing = things[things.length-1]
      console.info("clicking " + bestThing.name)
      things[0].e.click();
    }
    var timer = setInterval(clickBestThing, 5000)

Of course it's much easier to `power = 999...`, but this feels more like automation and less like cheating.