Can I get accommodation in the lodge/tea house in the mountain area?

It depends on where are you trekking and which season will you be choosing to trek to determine the accommodation difficulty. Nepal between September and December or March to May it is difficult to get accommodation but if you have guide or porter with you they will call and reserve before you reach to the tea house. Otherwise in general you can get easily accommodation on cost 5 USD a night in a tea house based accommodation.