It is uneconomical to use Telekinetic Grab to retrieve bronze arrows, unless one finds 19 or more arrows on one square in an inaccessible location, which is impossible since the stack limit of arrows shot to floor is 25.
Players can tell how many arrows are in a pile just by looking, provided that the number there is less than five. However, a pile of five or more looks the same however many there are, so it could be any number from 5 to 2,147,483,647 (the maximum number of any stackable item that players can hold in a single inventory slot) arrows on the ground.
On the 7th of March 2011, these arrows were subject to a severe rise in price, causing them to rise to prices of 6,223gp per arrow. This caused mass buying in archery stores because they were a much cheaper price in those stores, then people would sell thousands of them for millions of coins. Often, nobody was able to sell any of their arrows for the actual guide price. Later that day the price was changed back to 7 coins, and then reverted to the original price, 18 coins, which means the high price was most likely a bug.