Lessen your quality on jpeg...
or Reduce you colors count...
In the following link (two pics 99K and 66K), I only reduced the quality of the JPEG.
You might say its a bit darker, but you can up the brightness a bit.
http://www.gregfolkert.net/pics/drook/
Saving at least 1/3rd in image size... with just a weee little bit of processing. Might just be worth that $700/month.