Are there any good services , which do not need control panel to be installed. Our needs are quite simple in our php script server. first security hardening + apache mysql php installation and optimization. then we would need only full time monitoring and security updates sometimes. budget around 50
dollars month. OS is Centos.

Hi,

Check out the System Management Offers and email the providers and ask if they can manage your server without Control Panel as not all 3rd Party Management providers offer this.

Regards,
Bobby

Do you have a server someone else (office, home, another data center) that you can use? If so, Nagios is great and free:
http://www.nagios.org/

regarding monitoring system I can recommend you http://www.panopta.com/.

For monitoring, you can also check out Zenoss www.zenoss.com