When you enter into online world, only website creation is not important. The website should be updated frequently, so that more and more people visit your website regularly. Fresh and updated content keeps visitor's interest intact for your website so they keep coming back to your site. Also the website should function properly so it needs be checked and maintained regularly.
Such updated and well maintained sites boost the search engine ranking as well. So I feel don't just pay attention to the one time website development. Give more attention to the website maintenance once it is done and made live.
As far as costing is concerned, maintenance services are not costing much now a days, we only need to check the maintenance plan carefully and select as per our need. Also see what all services we are getting in a maintenance plan.
I personally feel hourly maintenance costs more if it is calculated carefully. Any other alternative to this?