I heard a rumor that an RCA 359 field test set went for over $40K about 10 years ago. RCA shipped some RCA 359 sets to Russia. There is one at the ETF museum which I believe was used for testing broadcast transmissions around NYC.
http://www.earlytelevision.org/rca_rr-359.html
As in other antiques and collectibles the history of a specific set makes it more valuable. Probably a specific set which Elvis or JFK actually watched in their home would appeal to collectors of their merchandise. I bought a camera tripod from the Farnsworth museum which closed in Indiana which they said one of Farnsworth's original camera's sat on. I only paid $125 for it so not all old and rare items are worth alot. I got a photocopy of the Tripod on a Guitar magazine cover from the 1930s with it. I searched the internet and bought a copy of the actual magazine which also had a story of the Farnsworth corporation televising a guitar school.