Moddbox sells a reasonably priced supercharger kit that can get you roughly 80 or so HP. But, as has been said already, you would get better performance doing a V-8 swap on it. And for less money. I like my little 4.0, but it doesn't get my pulse going like it's big brothers would.
I guess it all depends on what you want to do with the car, what your skill level is and now much you can comfortably spend. The moddbox kit doesn't require a ton of skill. Honestly the V-8 swap doesn't either, it just takes a lot more time and work. Aftermarket for the 4.0 is almost nonexistent too. Good luck finding a good performance cam for it. A tune will be probably needed in order to get the most out of any mods, so factor that in as an additional cost.
Just buy this and swap everything out.
https://clarksville.craigslist.org/cto/d/clarksville-2007-ford-mustang-shelby/6791117172.html
I guess it all depends on what you want to do with the car, what your skill level is and now much you can comfortably spend. The moddbox kit doesn't require a ton of skill. Honestly the V-8 swap doesn't either, it just takes a lot more time and work. Aftermarket for the 4.0 is almost nonexistent too. Good luck finding a good performance cam for it. A tune will be probably needed in order to get the most out of any mods, so factor that in as an additional cost.
Just buy this and swap everything out.
https://clarksville.craigslist.org/cto/d/clarksville-2007-ford-mustang-shelby/6791117172.html