Enable Website online/offline in Magento website

Hi,

I would like to be able to Enable my Website go online/offline as & when maintainenece work is going on in the back end.

I believe Magento does not have that option? but a Word press directory creation in Magento can facilitate that?

Please advise:

1. Your expertise in that matter.
2. Time to do this job
3 Total Cost (NOT hourly rate) for this task.

Thanks
Regards
Terence