Are you looking to get a brand new V6 Mustang??? Unless it's brand new, I wouldn't bother. Even still for what the brand new coupes go for you can get a gently used GT or Cobra.
There are lots of mods for the V6 Mustang. I friend of mine bought one in 2001. Put a dual exhaust on it. Sounded pretty good.
Couple places to check out:
http://www.extremev6racing.com www.v6power.net --Matt