Regular buses from Vilnius and Kaunas are the best way of getting here with the ticket setting you back in the region of 20-30 Lt.
Kautra (http://www.kautra.lt) is a bus company operating out of Kaunas. Be aware that these are not the only buses out of Kaunas.
Both Vilnius and Kaunas buses take approximately 2.5 hours and depart every 1-2 hours between 5.30AM and 7PM.
