I assume you have access to a windows computer ?
1) if you only work a couple at a time, download FREE Irfanview and use the "Image>Resize&Resample" and pick one of the standard sizes like 800x600 pixels or 1024x768 then "File>Save As>" but it's only one at a time. Either of those choices will reduce the photo down well below 300k each, usually about 150k.
read about it & download it from
http://www.irfanview.com/2) Do batch (whole folder if you like) resize & rename (watermark & other manipulation) with FREE FastStone Photo Resizer
http://www.faststone.org/FSResizerDetail.htm