I don't know if it was the case this time. But, I have noticed that a lot of sellers start out a listing very very cheap and the put the price up after a few sales.

I believe they do this for two reasons.

Firstly, and most obviously, to gauge the market to see how much they can sell it for.

But most importantly to get some "sales history". Once they've got the sales history and have got their listing to the top of best match rankings, then they put up the price. It's actually a very smart tactic if you are planning to sell hundreds of the same item.

However, the difference in prices of your item shows it most probably was an error.

In relation to sending more money, I wouldn't worry about it. If they have sold 140 at that price they've had plenty of time to wake up if it was a mistake, and as you said, you only bought it because it was cheap.