As per your requirement, it seems to a week's work. We have already worked on such projects which are totally CMS based. The technology on which we work are : Dot net(2.0,3.5),PHP,AJAX,WebServices, SQL Server(2005,2008), MySQL, PDA, iPhone. So we can easly go with the technology in which your site already exsist. We have been doing well in this field from more than 4 years with 100% client satisfaction. You can contact us through skype (itgc007) for detail discussion before making any decision.
Cheers