While the Su-30 aircraft are relatively cheap, at $30-35 million each (half what a comparable Western aircraft would cost), the Russian models have reliability and durability problems their more expensive Western counterparts dont. For example, this year, India had problems with the engines on its Su-30s, and it turned out to be pebbles on the runway getting sucked into the engines when the Su-30s landed. The Russian fix was to make sure the runways were kept clean of pebbles.
There are other Sukhoi aircraft as well. The upgraded Su-25 ground attack aircraft, now called the Su-39, looks good on paper. This 21 ton aircraft can carry six tons of weapons and deliver smart bombs in at night and in all weather. But theres not much of an export market for a high tech ground attack aircraft, and the Russian air force is not interested either. The Su-24 all weather bomber is another good design that has no new markets. There is, however, business in upgrading and rebuilding existing Su-24s and 25s.
Sales of Su-27 type aircraft are making it possible for Russia to at least try to build next generation aircraft to compete with the American F-22 and F-35. The continued production of the Su-27 and its variants also maintains Russian capabilities for building high tech combat aircraft.
Russias last best hope to stay in the combat aircraft business is found in the Sukhoi organization. The 1970s era Su-27 (the Russian answer to the F-15), entered service in the 1980s, but fewer than 400 were manufactured before the Soviet Union, and orders for Sukhoi aircraft, collapsed in 1991. But the Sukhoi designers were resourceful, and developed variants of the Su-27, and several in the Su-30 series were very successful when sold to India and China. While most of these sales are for Su-30s to be assembled in China and India. However, there are enough orders for complete aircraft for Russian plants to move from building 36 Su-30s a year to 48, or more.