If you're craving a recipe with a particularly expensive ingredient, you may still be able to afford it on your budget. You just need to make a few substitutions. Recipes for soups, tarts or soufflés may call for crème fraîche, which is very expensive. Instead of splurging, simply substitute with an inexpensive alternative like sour cream. If you're making an Italian dish that requires mascarpone cheese, use cream cheese instead. You probably won't even notice the difference.
Fresh herbs can also be expensive. If the real thing is out of your budget, use dried herbs instead. If you buy them bagged from your local ethnic store, you'll probably get an even better deal. Just make sure you research to find out the proper measurement substitution -- dried herbs are usually much more potent than fresh. If you're not sure what other expensive ingredients can be easily substituted, you can probably find out with a simple Internet search.