From the custom milling end of things with a little knowledge of the anno pricing...
Custom work costs money. If it gets really complex the price tag goes *WAY* up... Same idea with custom anno.
All that being said... Consider what you have for a budget. Make sure you have ideas in mind before contacting a machine shop/airsmith/anno artist. These ideas are the only way for one of these people to give you even a ballpark figure for the work you want done.
If it turns out that completely custom is too expensive (And it might just be) consider looking around for a production body you like and working from there.