Seems to me that this could get extremely convoluted in a second. Cost estimating is a sub-process of bidding, which is a sub-process of sales.
If we treat every sub-process as a macro process with performance indicator expectations, we can create a bureaucratic nightmare, with no end. An organization can have a very effective cost estimating activity and lose all bids. To me, it makes sense that the cost estimating is assessed as component of the sales process. If our sales goals are not being reached, it can be attributed to many factors, accuracy of cost estimation being one of them.
Be very careful if you expect to see KPI's (or any means of process effectiveness) for every micro or sub-process. You might doing your organization a disservice.