Aero Mongolia flies from Ulan Bator to Irkutsk 4 times a week. Alternatively, Mongolian Railways (MTZ) operates a train from Ulan Bator to Irkutsk 4 times a week. Tickets cost $55 - $75 and the journey takes 43 h 4 min. Russian Railways also services this route once a week.
From Ulan Bator drive to Ulan Bator airport, fly to Irkutsk airport, then taxi to Irkutsk. 1 h 50 min $451. From Ulan-Bator train to Irkutsk Passajirskij. 43 h 4 min $65. From Ulan Bator drive to Irkutsk. 14 h 32 min $76.