I've finished Lungfishopolis, blown my stash of arrowheads on the magnet-thing and a couple of psy cores, and just started the Milkman Conspiracy.
And now I'm suddenly shown a warning that says "You should have the Cobweb thing, or you won't get far in the Milkman Conspiracy." It costs 800 arrowheads. I just spent all of my arrowheads. I am sad. (And I've tried doing the Milkman Conspiracy anyway. I can do some stuff, but I need some particular items to get further in the game. Those items are, as far as I can tell, behind the cobwebs that block off some of the houses.)
I've already bought the dowsing rod and dug up about a half-dozen deep arrowheads, so that source of easy money is already partly depleted. Is there any other way to make 800 arrowheads in a relative hurry? I'm not particularly fond of grinding; I've only earned a cumulative total of around 500 arrowheads so far.