Oh man, I am going through the same process! A voice changer system is so nice to include- especially if you want to be heard while at a convention! I'm not very proficient with the electrical work needed to program a custom sound board, however, I had nice success with a VELLEMAN MK171 Voice Changer kit from amazon for about $15. it has a mic port, and a place to wire in a different speaker. the downside for me was the large amounts of feedback i got. I then switched to a premade kylo ren voice changer also from amazon.- it comes with a headset mic and a small hardwired speaker which is small and light enough to fit in your helmet. what I chose to do however, is run that kylo ren changer not from its pre-wired speaker, but instead into a portable amp (used for walking tours/classrooms) that way its loud as well. however... if price were not an issue i would totally buy one of those stormtrooper voice systems the guys in the 501st legion use.
WH40K Pepakura File Library 
