If you save with the 'create PDF-compatible file' option, your images will be embedded anyway (in the PDF portion of the .ai file). If what you call 'bitmaps' are highly compressed JPEG images, the embedded data (in the PDF portion) can balloon to many times original file sizes.
You'll find that embedding color (ICC) profile also adds to file size.
I see. Although I'm still not sure why the .ai file is several times larger than the images combined. Thanks for the tip!
Although I'm still not sure why the .ai file is several times larger than the images combined.
See my edited response for a possible explanation. Are your images JPEGs?
Yeah, they're maximum quality JPEGs.
Open one of the JPEGs in Photoshop and save as an uncompressed TIFF. That'll give you an idea of uncompressed image file size. (It will be larger than your JPEG file size, regardless of the quality level of the JPEG.)
Illustrator will use some degree of compression in creating the PDF-compatible portion of an .ai file. However, the basis will be the uncompressed image size, not your JPEG file size. Depending on your JPEG compression level, therefore, it is entirely possible that your .ai file size ends up considerably larger than what you might expect on the basis of the JPEG file sizes.
Again, this assumes the use of the PDF-compatibility save option.