Go to Google and Search for North Sikkim Share in base package it will come around 5-7k for 3-4 night and days .
you will find what you need they will take you to the most incredible places in Sikkim
Here are some lovely offbeat spots of Sikkim
Borong
Rolep
Chalamthang
Hee Patal
Kaluk village
Yakten
Sajong. Reshi hot spring
Yumesamdong hot spring
Singtham village visit
Ravangla Buddha park
Aritar is mesmerising town of Kanchenjunga
Rinchingpong view Reshum village.
Many places are cover in sikkim, mainly sikkim is divided in to south and north sikkim, in south u can cover Gangtok, Nathulapass, in North sikkim we can cover lachun, lachen zero point, yumtung valley, kalapatther.