Since centos, cpanel and dovecot are all open source, so free, it seems to me that you can't get it cheaper. And for better, you would have to tell what's not good enough in your current setup.
Hey
i need your help for the best performance of sending an email,
check this server:
centos 6 + cpanel + dovecot + 10 additional ip + 15 domain
i want to configure sending email service which can switch ip and domain for prevent any spamming result in gmail or etc,
this server is use for our company newsletter,
i have configure all general setting like rdns spf and dkim, Is there something else similar or better/cheaper?
Thanks for any advice.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic