I'm not going to read all the replies so this has probably been said.  I have two 1,000 bushel pits spaced so I can dump without moving.  Two pits was not twice the cost of one but I don't remember how much less the second one was.  It still seemed like an expensive luxury at the time but I realized after the first day using them that it was a huge efficiency thing.  Now, the limiting factor for dumping is how fast I can open the traps and how large the traps are.  I can open my traps, poke my head in the dryer shack to check it out, close the traps be back on my way to the field in less than 3 minutes.  For my operation that is worth an entire extra truck and driver.  It means that 3 people can keep a class 8 combine with a 12 row corn head moving in 250-280 bushel corn for all fields that are within 3 miles of the bins.

So if the second pit costs $30,000 you should weigh that against the cost of a semi truck, its operator, and the never ending maintenance they require.