Bandwidth Monitoring by IP

Hi all, Does anyone know of a low-cost solution for monitoring bandwidth by IP? My original thought was 1 switch port = 1 IP, but in the case of virtual IP's on a single port, that just wouldn't work. I'm seeing more and more of a demand for a basic BW report by IP, so our customers can bill their customer accordingly. Any recommendations? Thanks, Dan Dan Mitchell Internet Systems Engineer - Boston AllegianceInternet / Hosting.com 781.478.1857 Direct Line dan.mitchell@hosting.com