While the reply letter is probably personally satisfying, it is irrelevant. She is trying to equate cost with price. While they are related, they are not the same thing. Cost is the amount of money and and time it takes a vendor to create and deliver a product or service. Price is the amount of money a customer must spend to acquire that product or service. The only required relationship between those two is that over the long term course of business, prices must exceed cost if you want to stay in business.
But once that requirement is met, there is absolutely no obligation for price to be related to cost - i.e. just because it costs me $1.00 to build a widget, there is no obligation on my part to sell it for $1.10. If my widget is something that revolutionizes the planet and the lives of the people on it, and everyone on planet Earth wants one, I'd be insane not to sell it for $100 if that's what people are willing to pay.
Because at the point of sale, the only real attribute that matters is the perceived value the customer places in your product or service. When someone complains, "Why should I pay X when it only costs Y to build?", what they are really saying is, "I don't think that thing is worth X."
What the complaining bride is really saying is she just doesn't think wedding photography is worth $3,000. In the same way, if you went to a car dealership and complained about the price of the model you wanted to buy, you wouldn't get a lecture from the salesman about how much it cost to build the car, ship the car, insure the car while it's on the lot, cover his commission, etc. He's try to sell you on the "value" of the car - the smoothness and quietness of the ride, the collision safety, the reliability, maybe even the status associated with the driving that model.
At which point, one of two things will happen. If he sells you on those values and you have the money, you'll buy the car. But if he doesn't sell you on those values, you won't buy it, even if you have the money. Because you don't think those values are worth the price. At which point he'll steer you over the corner of the lot with the clown cars on it.
If a prospective customer balks or complains about your prices, you have one of three choices:
1) Successfully sell them on the value of your product
2) Lower your price to match their value expectations
3) Redirect them somewhere else where they can buy at a price that matches their value expectations
Having said all that, I have a sneaking suspicion that the bride wasn't really complaining about supposedly overpriced $3,000 wedding photographers. She claims she can find someone who will do the job for $400. Fine. Why then isn't she just shutting her trap and hiring the $400 photographer. The answer seems obvious. She's looked a the work of the $400 and $3000 photographers, respectively. She realizes by any measure of evaluation that the $3000 photographer is infinitely better and will deliver a vastly superior product. She WANTS the photos created by the $3000 photographer. The $400 photographer? Not so much. So what she's really pissed about is the fact that the guy whose work is clearly superior but costs a lot more won't lower his prices to meet those of the guy she knows whose photos are going to suck but is charging what she is willing to pay.