Steve likes to watch streaming on TWiTCH, and one streamer was able to use his keyboard to change his voice while narrating using a device called the TC Helicon. How does he do that? Leo says that a voice changer is usually the way he'd do it. The better ones do cost more.
There's probably a way to build his own using a Raspberry Pi. The Chatroom says that NCH Software has a voice changer for Windows. It costs $25. Leo recommends trying Screaming Bee MorphVox Jr.. He can try it before he buys. There's also a Pro version.