Hie Himanshu...glad to know your choice to visit Gangtok bcoz it's truly an amazing place..u will definitely enjoy it like a bliss if u are a nature person coming to your query.. December being a little off time to visit, u will surely have lower tariffs everywhere. however you can land up at hotels like Tiptop which serves good food too and it is at walking distance from main market. also u can book a tempo traveller from the taxi zone itself. But don't forget to bargain with them.