I spent an hour assembling an MK171 digital voice changer kit from Ramsey Electronics for my Mysterio costume. The plan is to place the microphone on a wire inside the glass sphere with the speaker mounted outside so that I can communicate. I will probably have a head operated button inside that gives me push-to-talk capabilities. I picked the voice changer kit because I felt it would give me more options than a simple amplifier.
Although the voice changer kit only cost $15, I still have to purchase an external speaker to use with it.

Depending upon the acoustics of the sphere, I may also need a microphone outside with an earphone wire running inside to hear people talking to me.

I spent a much larger amount of money on an LED strobe light kit, which will hopefully drive flashing lights from Mysterio’s cape clasps or sphere.