[Exim] Best antiviral solution for Exim?

Hi All,

I'm trying to find a good commercial anti-viral package that will
integrate well with Exim. The problem that I'm having is that all of
these antivirus software salespeople are trying to sell me products
aimed at those who want ready-made solutions. They want me to buy their
stand-alone mail servers that will scan and relay mail to my existing
servers. I'm having a hard time finding a good product that will work
with Exim at a reasonable price. Here are the requirements:

- command-line scanner (or daemon)

- the ability to automate updates of virus signature files

- a pricing structure that is not based on the number of employees,
workstations, or e-mail accounts that I have

Is there such a beast? What are other Exim users using?

thanks,

Chris