I emailed a 737 captain I know, he also happens to be #1 seniority for Continental at EWR on the 737. Here's his response:
Regarding your question about a go-around in a 737, let's consider in round numbers that it might take 500 to 1000 pounds of fuel (6.7 pounds per gallon; maybe 80 cents to $1.00 per gallon these days, depending on where you are) depending on whether or not you can just do an overhead pattern with the tower or get cycled back into a radar pattern with approach control. Yes, there is the crew cost per minute....I'd say a go around might add 10 minutes to 25 minutes onto the flight. My pay at Continental is $166 per hour. Maybe the first officer is $120 per hour.....I am really guessing here.....and the flight attendant pay something much less. Anyway, there is also maintenance costs that a factored in per hour, as the extra flight time on a go-around would put the airplane that much closer to the next scheduled inspection. There would be some maintenance cost per hour to consider as well as direct operating costs like the fuel and crew costs.
There might be other costs to the airline if the go-around resulted in mis-connecting passengers. You could probably extrapolate your problem and let it have various subcategories of consideration. If the prof only wants direct operating costs, you can probably do a credible job of estimating those. Realize the crew costs are much higher at a Delta, American, or United Airlines, by the way.