How the system works...
In 1965 the British Antarctic Survey requested the purchase of a ski-equipped Skyvan, total cost £160,000. However the Treasury ruled that this was much too expensive and instead bought a Pilatus Turbo Porter ( cn 619, VP-FAN ) for £30,000.
In 1967 they bought a refurbished Norwegian Otter ( cn 395, VP-FAM ), cost unstated.
In 1968 they bought a new Twin Otter for £150,000 under a new policy of multi-engined aircraft for the BAS.
So probably about £200,000 spent in three years because £160,000 was too expensive. Such is the logic of govermment.
Oh and of course that all came out of foreign-currency reserves, instead of Sterling into the local economy.