Why going to spend a few hours on implementing SA, changing your set up and when everything is installed check and maintain the anti spam solution on a daily base? It is time consuming and results in a non profitable action in your company.

Maybe it's better to take a look at managed email security solutions like MX Lab. You can visit them at http://www.mxlab.eu. Such solutions only need an MX change and you are safe for viruses and spam, well for some 98%. You don't have to spend you time on installing and maintenance and you're server will be less under load when spam hits your machine.

Just my thoughts on this matter.