Ah, if only voice acting was so simple! Really, for best results, you get an experienced actor and you put them in front of a decent microphone. My experience is also that someone with directing skills is an enormous help in getting the best performance out of even a skilled actor. I've gotten good voice performances from plenty of people "off the street," but it is worth underlining that most of the time, using a pitch changer on yourself or getting your sister to read a few lines is a way of shorting yourself. If you are going to spend the time getting good textures, good renders, good models, tweaking the animation, etc., then you deserve a good voice actor as well.