The unique prototype of a Leica APO-Telyt-R 5/600mm lens is currently offered on eBay for EUR 140,000 (USD 157,000). Interestingly, the same lens was listed on eBay back in February 2015 for EUR 200,000 (USD 230,000).
The lens features a catadioptric design, a good description/review of the Leica APO-Telyt-R 5/600mm lens can be found at apotelyt.com.