Russia has introduced a new version of its Buk anti-aircraft missile; the Buk M3. This version has a longer range (75 kilometers compared to 50 for the M2) and improvements in the guidance system and overall reliability. Development of the Buk M2, a radical redesign of the 1960s era SA-6, was completed in 1988, near the end of the Cold War and disintegration of the Soviet Union. This delayed its introduction. Russia was not able to start production until after 2002. When NATO discovered the Buk M2 they called it the SA-11.
Buk began development in the 1970s because of the success of SAM-6 system in the 1973 Arab-Israeli war. The Buk M1 entered service in the 1980s while work got underway for the even more advanced M2 and M2E. These were the ones delayed by financial problems in the 1980s. The M2 missiles weighed 720 kg (1,587 pounds) each and have a max range of 50 kilometers. This was followed by a lighter (581 kg) version with the same range. The missiles were carried and launched from a tracked vehicle that held four missiles. Another vehicle has the target acquisition radar which has a range of over 150 kilometers. Versions of the Buk were developed for use on ships.
As successful as the SA-6 was in 1973 and U.S. and Israel quickly developed electronic countermeasures. Russia responded by improving Buk but was never able to repeat the success of 1973, which was largely the result of Israel underestimating the SA-6 and the ability of Egyptian crews to operate the systems. Israel has not repeated that error since then and it was a wakeup call to the United States and other NATO countries as well.
An example of this could be seen in the 2009 decision by Finland to replace, at a cost of over $700 million, its three year old Russian SA-11/17 (9K37 Buk M2E) anti-aircraft missile systems, with Norwegian NASAMS. Norway developed this system in the early 1990s and deployed the first missiles and radars in 1995. NASAMS uses the American AMRAMM radar guided air-to-air missiles fired from a six missile container. This ground based AMRAAM weighs 159 kg (350 pounds) and has a range of 30 kilometers (it's radar can see out 50-70 kilometers), and can hit targets as high as 20,000 meters (65,000 feet). What makes the AMRAMM so effective as a SAM is the capabilities of its guidance system (which is about two thirds of the $400,000 missiles cost.) Testing also revealed that AMRAAM could be used to shoot down cruise missiles.
The Russian Buk M2E missile had a range of 30 kilometers. Even with upgrades, the accuracy and reliability of the AMRAAM is superior to the Russian missile. The AMRAAMs are protected inside their canister (Buk missiles are not), which means fewer maintenance problems. The Buk is combat proven, having been used in Georgia during 2008. Both Russia and Georgia used their Buk systems to shoot down aircraft and UAVs. But the Finns believe the AMRAAM (also combat proven) based NASAMS is a better long term choice. There's also the suspicion that Russia may know things about defeating the Buk that they are not sharing with the Finns. Norway pioneered the use of AMRAAM as a surface to air missile.
The Finns received the Buk M2Es in payment for the $300 million debt that would have taken much longer to get paid off in cash. Russia has paid off many of its older (often Soviet era) debts with modern military equipment. Some of the recipients have found that the stuff wasn't modern, or effective, enough.