ok lets see... all I did was turn off some services in the background I did'nt need, add on some free software (Zonealarm, AVG, Spybot and Adware), schedule AV and Malware Scans for 2am when I'm nicely asleep and thats about it... as to constant vigilance, I just don't open attachments unless they are scanned first and thats about it..

total cost to maintain : Free.
total time to maintain : for the scans 2 hours while I'm asleep and maybe 5-20mins a week awake.

ain't hard to do...