Ukraine's economy was never reformed after the collapse of communist and is still run by a bunch of communist era politicians. The economy is a mess and Ukraine is always behind in its payments to Russia for natural gas supplies. Russia says it is buying the missiles to augment it's ICBM force, although it is also known that the government is having a hard time affording its new, solid fuel, Topol-M (SS-27) ICBMs (which cost about $52 million each). The thirty UR-100 missiles were probably obtained in trade for large quantities of natural gas supplies.
The hundred ton, liquid fueled missiles were designed in the 1960s and early 70s and began entering service in 1975. The missile carries six warheads and was continually updated and well maintained. Some UR-100s have been used as satellite launchers, and in that role can place up to 1.85 tons of satellite in a low earth orbit.
Ukraine is selling Russia 30 UR-100 (SS-19) intercontinental ballistic missiles. When the Soviet Union dissolved in 1991, all weapons were considered owned by the newly established countries they were in. Ukraine thus obtained 1300 nuclear warheads and 190 ICBMs. Under a disarmament deal, Ukraine turned the warheads over to Russia for disassembly. The United States paid Ukraine $500 million to help destroy or dismantle all the missiles and launch facilities (silos, control and maintenance facilities) it had inherited. The last UR-100 missiles were thought to have been destroyed in 1999. Apparently not. In 1991, Ukraine had 130 of the 360 UR-100s manufactured through the 1980s.