Just out of curiosity I took a current snapshot of memory use using TaskInfo2003

Avast Antivirus Service:
InMemKB 6640
PrivateKB 6412
TotalKB 17,796

Avast Email Scanner:
InMemKB 4616
PrivateKB 3988
TotalKB 15,068

Avast is set up to run Internet Mail and Standard Shield.