I'm a bit late to the short discussion here, but I thought I'd mention the Contemporary Frame company. They sell Nielsen frames, and they also offer their own more economical line of "house brand" frames in a few Nielsen-like styles and in a large variety of colors and finishes.
I just bought a dozen of their C911 frames, the same profile as the Nielson N11, in 13x15 lengths, and I'm really pleased with them. They are very precisely cut and are of very high quality. I can't directly compare them with Nielsen N11 since I've never bought any Nielsen frames, but I'd say you can't go wrong with these frames from Contemporary.
Their web site isn't much, just a place to register so you can download a PDF catalog of their stock. But they'll send you some color brochures if you call them. http://www.contemporaryframe.com/