Searching on Google for the keywords "star of David" Ebay retrieved about 282,000 results, which means that it is a very popular item on eBay.
Clustering the first 150 results on vivisimo shows the main categories of these products:
38 results deal with Jewelry
24 results deal with Ebay Store
12 results deal with Designer
9 results deal with Crystal
7 results deal with Symbol
7 results deal with Star of David necklace
8 results deal with Italian Charms
6 results deal with Heart
4 results deal with Magen David
5 results deal with Books
Searching on Ebay for the keywords "Star of David" retrieved 668 items:
Jewellery & Watches (385)
Necklaces & Pendants (163)
Charms & Charm Bracelets (74)
Religions, Spirituality (148)
Historical Memorabilia (6)
Decorative Collectables (5)
Pottery & Glass (43)
Pottery & China (3)
The overall picture is that the most popular items are Jewellery, Necklaces and Charms.
I'd like to read an analysis of the Star of David world market. Maybe one of you readers can guide me where to find it. Then I'll have an answer for the question – How much does it cost?