Make sure you are comparing similar sails - type and weight of cloth, number of reefs, number of full length battens, etc. Generally the lofts buy their cloth from someone else (like Challenge) and then may put their own name on it. Premium dacron of the same weight will be pretty much the same.
I note you are from Hong Kong. Rolly Tasker in Thailand is a huge operation with a reputation of building very good sails for good prices. Look for a local dealer.