Something a lot of us forget is that saving money isn't just about paying less; it's also about making use of everything you buy. There's no easier way to raise the cost of a meal than to let half a pound of asparagus rot in the fridge because the meal you made only called for eight spears.
Plan your meals so you'll use up all the perishable ingredients you buy, especially the more expensive ones. If you'll be making scallops with a raspberry reduction, plan to make a raspberry-pecan salad the following night and raspberry yogurt parfaits for Sunday breakfast.
After that meal of filet mignon, you can make the extra potatoes and green beans into a stew, a casserole and a potato salad to serve with burgers -- all in the course of a week, with hardly any sense of repetition.
If you prorate the cost of your ingredients over several meals, each one ends up costing you less (if you buy in bulk, this approach is pretty much essential to make the savings real). This can also involve choosing one very special ingredient and incorporating it into your splurge meals until it's gone. If that lobster mac and cheese calls for truffle oil and you simply can't leave it out, plan to make your special meals revolve around truffle oil for a while. This won't be a hardship.
There's another option, though: What's just as good as truffle oil?