If you're a Flex developer, I say Flex 100%. Otherwise, I'd say you should write your own with whatever language you're most comfortable. I think you'd have to do so much work to Wordpress to make it like your client is wanting that it wouldn't be worth the effort.
I am about to make a website for a real estate company that wants online listings of all homes.
My question is, which would be better to base the website on: Wordpress or Flex/Flash...
For Flash/Flex I think something similar to http://www.volkswagen.co.uk/used/search might be good.
Please let me know your opinion...