I'll echo the option for hiring someone, if possible.
That said, zplane's
elastique is quite good. You can test it out using the fully-functioning demo version of
Reaper using the
ReaPitch plugin. You can change the
pitch and
formant values to change the sound of your voice.
You can also try out Antare's
Throat EVO, which has a demo but requires an iLok account.
By way of explanation, pitched sounds are being generated by passing glottal pulses produced by your vocal cords through your vocal tract. By adjusting the position of your tongue, you divide the tract into a series of chambers. Each chambers create resonances - called formants - which is how we create distinctive phonetic sounds. The position of the formants is basically a function of the length of your vocal tract.
For example, the position of the formants for an average male /EE/ sound are located at 270, 2300, and 3000Hz. Since these formants are a function of the length of the resonating chambers in the vocal tract, their position doesn't change when the pitch changes.
Pitch shifting by
only speeding up or slowing down the sound shifts not only the frequency of the voice, but the frequency of the formants as well. That effectively changes the perceived length of the vocal tract, which is where the "chipmunk" or "giant" sounds come from.
To prevent this, pitch shifting software automatically readjusts the position of the formants so they
don't change as the frequency changes. This allows you to change the pitch without altering the perceived size of the speaker's vocal tract.
ReaTune (and most other pitch-correcting software) allows you to do the opposite as well: move the position of the formants without altering the pitch, changing the perceived size of the vocal tract.
There are other factors that can be adjusted as well, such breathiness, tenseness, and so on. Some programs basically reconstruct the vocal signal from scratch, and allow you to replace the glottal pulse with a synthetic one.
Throat EVO is one of the programs that allows you to modify these parameters.
Of course, you can modify the quality of your glottal pulse yourself, without any software.
Depending on your needs, if you "create a character" with a different cadence than your own speech, alter some of your speaking patterns, and shift the formants and pitch to taste, you
might be able to create an effective different voice.
But if you expect the software to be able to do most of that, I think you'll be disappointed by the results.