Try these agencies, I find travelpresident is cheap in comparison. All the best...

http://lowestfare2nepal.com/index.html

http://travelpresident.com/?page=c3BlY2lhbEFpckZhcmU=&lang=en

http://flyeverest.com/promotionalfares.asp

http://peacelandtravels.com/

http://fly2nepal.com/