If you don't want spam in your inbox, use your choice of SMTP blacklists (AKA "RBLs" and "RHSBLs") and a good filter -- I use DSPAM for those who get past my long list of 17 SMTP blacklists. I see one or two spam messages per month in my inbox, and my total cost was my time in configuration.

If I didn't run my own server, I'd still use those blacklists, but via a homegrown bit of perl, then pipe the remaining messages into DSPAM. I recently set my dear old mom up like this, and it seems to work just fine.

Nuthin' to it but to do it, and the price is right.