THE CHEMICALLY FUELED BLACKBIRD WAS A RIDICULOUS PLANE.

The dangers of in-air-refueling, operating costs, range and mission limitations of a chemically fueled Blackbird are utterly absurd. So, absurd that a nuclear powered bird is the only thing makes sense. 

JP-7 cost as much as an expensive single malt whisky (Darling) [1] [2].  Single malt whisky prices run from $100 to $100,000 a fifth [3]. If one conservatively assumes a price of $200 for a fifth, then the price per gallon is $1000 in 2019 dollars. Using the CPI the cost of JP-7 in 1965 would have been about $123.18 per gallon [5]. I could not find 1965 price information for single malt scotch whisky. This reverse approximation is reasonable.     

A Blackbird tank held 12,219.2 gallons of JP-7 and, in 1965 dollars cost approximately $1,505,161. Without aerial refueling the Blackbird had a range of 2000 nautical miles. Missions often went over 12,000 nautical miles (Graham 38). Therefore based on a lower bound cost assumption for JP-7, a Blackbird mission of this length would have cost $9,030,966 in 1965 dollars. Or approximately the cost of 5 F-4 Phantom II's [4]. Or ten times the amount it cost to fill the 3 million gallon tank of a Nimitz class carrier. 

The supposed per unit airframe cost of the program was 34 million dollars. So, in as little as 3 missions the cost of the airframe would have been exceeded. If a Blackbird ran two missions per month then the yearly fuel cost of a single Blackbird was $216,743,192.06 or six times the cost of the airframe. The fuel cost for all 32 SR-71's was roughly 7 BILLION dollars per year in 1965 dollars. That's roughly 2% of the U.S. Defense Budget for 1965 [7] going to fuel the Blackbird. The 7 BILLION dollar figure is close to the 8 BILLION dollar cost given for Project PLUTO (Dewar 65) [8]. 



SOURCES:

1. https://www.456fis.org/BLACKBIRD_DETAILS.htm
2. Mayday!: A History of Flight through its Martyrs, Oddballs and Daredevils (Darling)
3. https://www.thewhiskyexchange.com/whisky/age/20-year-old-whisky?filter=true&rnd=2017168149#productlist-filter
4. https://en.wikipedia.org/wiki/McDonnell_Douglas_F-4_Phantom_II
5. https://data.bls.gov/cgi-bin/cpicalc.pl
6. https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird
7. https://www.infoplease.com/us/military-personnel/us-military-spending-1946-2009
8. Dewar, James A. To the End of the Solar System: The Story of the Nuclear Rocket. Lexington, Ky.: U of Kentucky, 2004. Print.

NOTES:
From source 1.
The JP-7 jet fuel is interesting in its own right: originally developed for the A-12 Oxcart plane in the late 1950s, it has an extremely high flashpoint to cope with the heat, to the extent that a match dropped in a bucket of JP-7 does not ignite it. The fuel also contains fluorocarbons to increase its lubricity, an oxidizing agent to enable it to burn in the engines, and even a cesium compound, A-50, which disguises the exhaust's radar signature. As a result, JP-7 is said to be more expensive than malt Scotch whisky, which gives some idea of how much a single SR-71 mission would have cost.

With only a 2000NMI or 2300 mile range the Blackbird that means the Blackbird only had an hour of useful flying time. The chemically powered plane is useless.