How do I write off the expense of a subcontractor that I paid less than $600?

I needed someone to work an event with me, to help speed things up, as my client asked for a second person.

I asked a friend also working the event if she knew of anyone and she referred someone to me, also giving her the wrong pay amount. I end up making $4 after the credit card fees when being paid by the client.

The subcontractor is being paid less than $600. How do I write off this expense, and will it be fully deducted, or only a percent, causing me to lose money on this "venture"?