The terms of your relationship with your contractor are governed by your contract. Your contract should specify whether your relationship is a cost plus, guaranteed maximum price, etc. Your rights to see the Contractor's costs (as well as its rights to claim additional costs) are interwoven with the type of contract that you have.

However there are a couple of different ways that you might approach it if you are looking to throw a statute at your contractor. If this is residential work, pursuant to NRS 624.600, you are entitled to know the identity of all subcontractors who work on your project. Therefore you may be able to obtain the information from the subcontractors. Furthermore your contractor is usually required to document any additions or deviations from the contract via change order, which should set forth the bases for the additions. If this is a residential pool/spa contract, there are very specific disclosure requirements regarding change orders and disclosures for such contracts (see NRS 624.940).

If you have problems with a contractor refusing to provide necessary information, you can utilize the services of the Nevada State Contractors Board to assist.