You really have to be careful about the scan quality with labs. Most of them say the scans are high quality, but in fact are often at most 6 megapixel scans at 10 bit color depth. That is how they end up with file sizes of 4.5 meg.
I recently bought a "decent" (not pro) canon scanner with 48 bit color depth. At full resolution, a 35mm negative scan is 120 mb, not 4.5. 120 film will be 4 x that file size, so about 1 image per CD.
I live fairly close to Berkeley. Just for fun, I could scan one of your negatives on my canon and you could compare it to what you are getting from the lab scan. It would be fun to see if there is a useful difference.
BTW - here is another lab, kind of "pro" oriented.
http://www.4photolab.com/Pages/services01.html