Subject to this Part, the taxable value of an external non-period residual fringe benefit in relation to an employer in relation to a year of tax is:
(a) where the provider was the employer or an associate of the employer and the benefit was purchased by the provider under an arm's length transaction--the amount paid or payable by the provider for the benefit;
(b) where the provider was not the employer or an associate of the employer and the employer, or an associate of the employer, incurred expenditure to the provider under an arm's length transaction in respect of the provision of the benefit--the amount of that expenditure; or
(c) in any other case--the notional value of the benefit at the comparison time;
reduced by the amount of the recipients contribution.