You can use whatever parts source you like, but these sites I have found to be the most reliable and provide great service. Prices vary between sites, so shop all of them for the best bargain. The first three sites listed have helpful exploded view parts locator diagrams to assist with part identification and assembly.
If you do not wish to order on line, use the part numbers from one of the websites and go to your nearest appliance parts retailer. A drive belt is a common item that most appliance shops will carry in their in-store inventory.
I cannot quote you a price as you have not provided a MODEL NUMBER with your question. I'm assuming by the picture that this is an Amana washer, but there is no model number information listed with the photo.
If you have questions, or require additional assistance, please post back with a complete model number (usually located on a nameplate around the wash tub opening, or on the back of the operator console), so that I may be able to provide you with better assistance. I hope this helps you.