Over $100 including shipping, and a week to get from Australia. Plus any returns may be problematic, unless the seller can arrange an exchange via the manufacturer.
If you have not already bought then I would look at Stebel USA.
They list for $75 each. Price includes shipping and handling, and only Michigan residents pay tax.
http://www.stebel-usa.com/product/32...ct_Truck_Horn/
They have an email address and phone number on the site to answer questions before you purchase.