Sales and use taxes shall not be imposed on the gross receipts from the sale, lease, or rental of and the storage, use, or other consumption in this state of the entire purchase price of a motor vehicle purchased when the maximum amount allowed by law is contributed by the United States Department of Veterans Affairs or the Department of Health and Human Services for a disabled person. If the amount contributed is less than the maximum amount, the exemption shall be based on the portion of the purchase price contributed.