I've noticed this a few times and thought there might be a post about it but I can't find one.
The lowest price per unit (for example Tree poison) is said to be 345. but when you go to the 12 available auctions they range from 1725 to 1900 per unit. the calculation seems to be confused for lots of items in the same way. that also means when you go to auction that item the price it pre-fills with is based on that incorrectly calculated price. meaning you could sell for a really low price if you don't check the actual auction price first.
summary of all auctions: http://i40.tinypic.com/140diyp.jpg
all auctions for 1 item: http://i39.tinypic.com/ea2zkp.jpg
posting own auction: http://i41.tinypic.com/5y6feg.jpg