Quote - If it needs to be good, i.e for a commissioned illustration, I export it back to my modeller and subdivide and smooth polygons until it's right. I am not so worried about polygon count...

I know Sculptris and Marvelous Designer create delaunay tris when modeling, but I don't think they can convert quads to delaunay tris. Any ideas on an affordable program...?

Try exporting the dress from Poser as a 3DS file. Poser will convert it to tris. When you import the 3DS file back into Poser your dress will be in tris instead of quads. That should fit the budget