Some of the main things to consider there are the ratio of production output to employees of the brand, cost of materials/facilities/equipment, level of finishing, and complication. Greubel Forsey for example produces about 100 watches per year with 100 employees, and all of their models are limited production so the cost of development is significant. It's easy to see why their watches have such enormous price tags, the company wouldn't be able to exist in that form otherwise. I normally wouldn't consider things like advertising, brand history, etc. towards the value of a watch, but others might.