Windows: Just create a scheduled task through the admin screens that runs against a DOS .bat file with predetermined copy commands to an external, mounted location:
sample "copy.bat"
Code:
copy c:\temp\* g:\externaldrive\temp\
copy c:\hot_blonde_pics\* g:\externaldrive\i_like_pussy\
For unix, do the same with a shell script and a cron job. The only money you need to spend is for the external / additional drives.