If you have 80 pages of content much of which is high resolution imagery and your resultant PDF file is 216MB, that's less than 3MB per page (and with the Smallest File Size setting, 180MB, less than 2.25MB per page). If you have photographic type raster imagery (as opposed to raster images of vector-like content) on each page, you actually are not doing that badly in terms of PDF file size. You can't legislate the size of a PDF file. Considering that the original InDesign document is 25MB with links to the raster images, I cannot imagine any way that you are going to get the PDF file size down to 10MB.
In terms of image compression, your only choices are to downsample the images when exporting PDF. Significant file size loss occurs going from 300/450 to 100/100 or 72/72 and/or to specify lowest quality JPEG compression.
Just remember that (1) your on-line PDF won't be worth much if the image quality is very poor and that (2) although 72dpi for screen viewing was in vogue years ago, many screens now are effectively anywhere between 150 and 300dpi, i.e. requiring the same or better quality than you would use for print.
- Dov
I figured it out!! Phew...
I had 11 PDF maps included in the links. The maps were not particularly huge (0.7-2 MB, and one 4 MB), but they must have been carrying a TON of meta data. I saved the PDFs as PNGs and the final PDF export is now 30MB!! When I save as reduced, it is 5.6 MB (and it still looks nice). Score!
Thanks for everyone's time and input!