I have heard that booleans in Bryce are sort of weird. Doesn't turbocad 6.5 pro offer 3d booleans? I don't know any low-end NURBS programs. And when you do the boolean operation I don't think you are going to get a NURBS surface on the mold. The low end version of Cinema 4D might work, execpt for NURBS. Hopefully other people will have more useful ideas.