How do I use SourceForge.net for a low cost CRM?

I need a super low cost CRM that seriously costs me about $1/month/user. The lowest I have seen is $8/month/user. So, I thought I'd use open source.

I was sent to SourceForge.net and there see plenty of open source downloads but really would not put the time into testing any demo until I understood the total cost.

I hope to have thousands and maybe tens of thousands of salesmen. How does this impact the cost?

I still do not have my arms around this problem to even see if a CRM exists for me.

Thanks.