You could try this: First, select the preset that says "smallest file size".
Then, on the right hand side choose the "Compression" tab.
Set up your compression settings as follows:
Then save your image. Check the file size. I managed to get a 1.83MB AI file, containing lots of raster images down to 343KB with those settings. If that's not enough, reduce the resolution settings even more, or set the Image Quality to "Low". Reducing these will impact on the quality of any raster images quite severely, but that's the price you pay for keeping the file size low.
Of course if you have lots of raster images, you might not be able to get the file size down as low as I did.
After you have made these settings, you can save them as a preset. Beside the Adobe PDF preset (at the top right of the dialog), hit the save icon, and name the preset so it will be available for other projects.