http://cgi.ebay.com/NEAR-MINT-KODAK-...d=p3286.c0.m14 ("near mint" with case for $56)
http://cgi.ebay.com/Vintage-KODAK-RE...d=p3286.c0.m14 ("with Extras" for $51)
These were all in the $50 area, or less in a few cases. This only includes sales in the past amount of time that EBay will let you search. (I don't know how far back they look.) In the same time period, five Retina IIas went for over $50 (one of which was a Rodenstock glass model that went for beaucoup bux).
I also listed two more above that went for over $50, as they are close enough to $50 to warrant listing, IMO, given the "near mint" claim and the "Extras".
This search of completed EBay auctions does not include the models of Retina other than the IIa, of which there are several. Additionally, they are very common (I should change that to often very common, as there is always someone trying to sell tin as gold) and very cheap at estate sales, swap meets, camera shows, etc. in the $5 to $25 range. I don't think a very high premium would be paid for overhauled models of most cameras, let alone relatively cheap cameras. I certainly would not pay more for a camera that had "just been serviced". I do not agree that the cameras rarely sell for under $50. In fact, evidence would support that they sell for under $50 more often than they sell for over $50.