Migrate a website from joomla 1.0 to joomla 1.5

Hi, i have a website with lot of articles and a huge database in joomla 1.0 I need to migrate it to joomla 1.5 and keep the same template, same funcionality (there's a bridge with the vbulletin forum) trying to lose as less as possible. Please be precise with the offer because is a no profit company and i couldn't give you more than what agreed. Website is [login to view URL] Thanks