What can be considered under 61.113 (c) for passenger equipment?
Incidental costs specific to the passenger, such as O2 for the passenger's medical condition, may be paid by the passenger and need not be factored into the cost of the flight for flight sharing costs.

In your example, the Hobbs charge for the aircraft is the flight cost.  If the passenger wants a headset, or anything else that is not a flight expense, the cost need not be shared.  

Landing fees, navigation fees and the like are grey areas, and I would split those.  But something like a tie-down or hangar fee is not a flight expense, and the passenger may pay for in full.

If you read cases where the FAA has prosecuted pilots for conducting operations "for hire" or similar, they tend to be egregious.  

So in your example, $60 would be the right answer.  I would suggest that you could even split the cost of the charts you might buy for the trip.

As a final word, I would make certain that your passenger understands that you are just sharing expenses, not that they are "paying for a ride."