Why not just ask me how to make a real doll? I know that's what you want. There are cheaper seamstress/pattern dummies that are perfec for pattern makers.
http://www.sewtrue.com/Dressforms.html
$130.00 for a totally adjustable dress form. Every measurement can be adjusted.
Now, if you still want to proceed with a plaster copy... you're talking (potentially) several hundred, and about a week's worth of work. Not to mention that it'll weigh about twice as much as your wife... if not more.
If you want a real doll of your wife (or some other porn star) you're talking (potentially) thousands of dollars and many weeks to complete. The only way to make money at real dolls is to sell sub-standard dolls in volume.