Cheap SOHO AV or Network Scanning?

[[H]ard Texan]

I am helping a friend's Aunt and Uncle keep costs down on their new business network. I have a 24port switch and a Network storage device with a firewall on it too, but I need to have some sort of antivirus for the computers.

There are 24 computers for the site, and all of the pricing I have done for that many computers is from $600-$3000 depending where I look.

Since this is a startup, they have very little cash to spend, and that kind of money is just NOT there. Are there any cheap/free business alternative anti-viruses? Piracy is NOT an option, they don't need to be sued.

OR, can I set every computer on the network with full access to the c:\ drive (I know, it's not secure) and have one computer with a paid AV, scan all of the other computers over the network?

Are there any other alternatives?

Thanks for advice.

Cliffs.
1) Setting up cheap network for new business
2) VERY tight budget
3) Need anti-virus solution on the cheap