The idea of covering the cost of the meal is only a guideline, for those that want to give a gift, but do not know how much to spend. It is sometimes suggested that the guest cover the whole of the guests expenses the that couple spent on the guest. See below.
And really, when you think about it, how much would you spend at a nice restaurant, and going out for some entertainment after that? That could be a guideline too.
Really, it is no ones business except those doing the paying what the wedding cost. Guests should not ask what it costs for any reason. But most of us can come up with a estimate, knowing what venues and caterers charge for meals these days. Especially if you are from a small town, and invariably know someone who used a particular caterer.
And yes, I would give a gift that might cover the cost of the meal, and then some. The daughter of a friend got married, I gave her $70. I had never met her or the groom. They had a lovely catered gourmet chinese food meal from a local restaurant that catered in chinese. But it did not cost anywhere near $70, even with a cupcake from her her gourmet cupcake tree included [which rivers did not eat one].
The expectation is that a wedding is not someones birthday, that will be repeated year after year. It is an event that the two people are beginning a life together. We are supposed to be invited because the host knows we want to be there, and wish the couple well, and start them on their way in style.
And, you should never ever have pay for a meal at a wedding, guests are just that. The host pays..
The wedding gift is not mandatory, just good etiquette. And the cost of it should be dictated by your own personal finances, and perhaps how well you know the couple, or if you are related to them.