I wish to travel Tibet from Sri Lanka with small group in September 2015.i wish to know the cost.

Well, it's hard to estimate the fee you would spend in there, because you may have different demands and the fare for all may range from season to season. Besides, foreigners must join a tour if they want to travel in that region with holding Tibet Travel Permit.

Generally, it is best to apply for the permit through a travel agency. Well, I recommend Travel China Guide to you. You can consult them about all these questions and general cost. Here is contact: traveltravelchinaguide.com