Deer Creek Products, (765) 525-6181 has the Traditions .45 cal Philadelphia Derringer (item no. P1015) for $115. The picture looks a great deal like the CVA Derringer, which is also .45 cal.
I've never seen one in .50 cal. Deer Creek also has something called a Dandy Derringer on page 37 of their 2007 catalog; it is priced at $99. There is no catalog item number nor caliber listed. The description does say it has a "nickel barrel and lock with a white gloss finish stock"; the picture looks identical to the Traditions and CVA derringers. On the same page are a "Henry Deringer" in .41 cal with no item number or price and a "Baby Deringer Kit" for $139 with no item number. The picture shows an exploded view of the CVA Derringer kit.
Finally, Deer Creek also has the all metal Traditions Vest Pocket Derringer in .31 cal. for $126.