I'm sorry, but Royal Enfield Thunderbird motorcycles do not typically have hoods. The term "hood" is more commonly used to refer to the protective covering over the engine compartment of a car.
Additionally, the cost can vary based on whether you are purchasing a genuine Royal Enfield fuel tank or an aftermarket option.
To get an accurate estimate for the cost of replacing a Thunderbird fuel tank, I recommend contacting authorized Royal Enfield service centers or motorcycle repair shops in your area. They will be able to provide you with specific pricing information based on your location and the specific Thunderbird model you own.