Generally there are 2 basic ongoing costs to maintain your website once it has been implemented. These include but are not limitied to Hosting and Domain Name renewal 

Ongoing costs for websites are monthly or annual depending on your provider. Monthly Hosting fees can start from $9.95 per month and up while Domain Name renewal will generally be every two years however this again depends on your provider.

If you need to update your website and cant do it yourself you will have to pay your web developer for updates as an extra expense. If your website needs changing constantly then a content management website might be a better way to go.