Thanks for the note. We obviously have bulk rates that get competitive when you get to higher volumes. Feel free to contact sales@lob.com if you are interested.
One thing to consider is you are ordering 100s of the exact same postcard. If you had to print out 500 different postcards, each going to 500 different addresses that you had to write, then apply postage to all 500, all of a sudden your time saving becomes hugely valuable. Not to mention you need to shop around for a printer, handle the image and prepress process, etc.
I think you'll find that if you shop around to competitors we are very competitive and in fact beat pricing with other comparable APIs.