Russia is selling Kazakhstan 40 refurbished S-300 surface-to-air missile launchers, and, presumably, the four S-300 missiles that normally go with each launcher. The launcher is mounted on a semi-trailer truck. Each 7 meter long missile, with its sealed container, weighs about a ton. Kazakhstan borders Russia, Uzbekistan, Kyrgyzstan and China. So where does the air threat come from? Nowhere, actually. This deal is a feel-good measure that also provides Russia some protection from a long shot Chinese air attack via Kazak air space.
Russia is in the process of buying up to 200 S-400 surface-to-air missile launchers (each with four missiles) over the next six years. It is phasing out the older S-300 and S-200 systems. This would mean deploying at least 18 S-400 battalions in the next six years, and perhaps more than twenty. The S-400 is sometimes described as an improved version of the S-300. Basically, it is. This is how Russia prefers to develop weapons, making incremental improvements on a basic design, and doing so for decades if the system continues to be successful.
Roughly equivalent to the U.S. Patriot, the Russian built S-300 was known as the SA-10 to NATO, when the system first appeared in the early 1980s. S-300 missiles weigh 1.8 tons each and are 26 feet long and about 20 inches in diameter. The missiles have a range of some 200 kilometers and can hit targets as high as 100,000 feet. The missile has a 320 pound warhead.
Price was not mentioned, but since Russia trying to interest Kazakhstan in joining a closer military organization, similar to NATO, but led by Russia, it's doubtful that the Kazakhs are paying much. Probably a few hundred thousand dollars per launcher (with missiles) if that. Every four or so launchers has a radar vehicle and trucks with maintenance and repair equipment.