I understand your frustration; in the military I was limited to online exposure once every month or so (being underway at sea).
Hope you get it worked out.
At any rate, I suspect that you are grabbing the entire virus database.
Instead of grabbing the whole thing (which is essentially giving you redundant data), try simply updating the virus definitions via the following commands:
Right click the system tray icon of Avast to bring up menu.
Select "update", and click on "Engine and virus definitions".
*NOTE: If you are using Avast-4 your menu option may be slightly different, but the gist is the same & should be fairly intuitive: open Avast systray icon properties, click on update, select update virus database (or something like that).
Good luck in your endeavor, and maybe look into using satellite internet uplink (still too rich for my blood, I'm afraid, ha ha). $1000 to $5000 USD (monthly, I assume), but hey, if you can get enough people together to pitch in, you could all share the bandwidth. To be honest, I really do not know very much about satellite internet, but it doesn't hurt to look at options...
Take care!