Hi,
Mirza / Glenn
The 'fluff' or growl and rasp or as TC Helicon term it...vocal formanting is demonstrated on their website in the form of a couple of video presentations. You will need quicktime to view them but it shows off the effects really well.

Personally I would just go for the voice prism basic as it seems a lot extra for the formanting and you can always buy the add on card to upgrade the voice prism to a plus in the future.

There is a second hand voice prism on ebay at the mo here......

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=23790&item=2512679779&rd=1

.....with no reserve. Don't know how cheap it is for you guys in the USA but the price when converted to UK pounds looks good to me.

Best to you
Tony