Hey:

I'm afraid I can't speak to the quality of the ebay luthier planes,
directly. But I've carved several archtops myself with the gear I have at
hand. This includes mostly my set of bench gouges, but I do lean heavily on
the convex-bottom planes at several points during the carving. I have a
tiny flat-sole version I made myself out of rosewood, but for (nearly) out
of the box performance at a medium price point, you can't go wrong with
these two from Lee Valley:

http://www.leevalley.com/us/wood/page.aspx?p=57205&cat=1,230,41182
http://www.leevalley.com/us/wood/page.aspx?p=67716&cat=1,230,41182

The smaller one is a real beauty to use, but the larger one is actually
more useful. Think of it as a tiny scrub plane. I have mine set pretty
rank, and it really hogs out material, at least relatively speaking on the
scale we're discussing. It's a perfect follow-up after the rough gouge
work.

Greg Isola
Alameda, CA