I don’t know what avast version you are using, but my figures aren’t even close to yours and I have all but two (IM and P2P) shields installed.

The virus definitions database (avast\defs folder) takes up a great deal of this 140MB on my system and that is variable as new definitions are added creating a new sub folder with the contents of of the old one combined with the latest incremental update. Avast periodically does house keeping removing the old defs sub-folders. So if you had the current defs version and the previous version (pre-housekeeping), that could vary by 140MB up or down (in your case).