Hi Ali,
Recruitment Cost would be the sum total of all the expenses incurred while hiring eg Consultant's Fees, Print Ad Charges, Payment under Referral Scheme, Travel Related Reimbursements etc.
Tracking of recruitment cost through various sources of recruitment and comparing with results/responses helps tremendously in chalking out Recruitment Mix Strategy.
At the end of the day, everyone looks for speediest recruitment at the lowest expenses.
Hope this helps.
Tx,
Rajesh