I stumbled upon my favorite cookie recipe a few years back by being cheap. The one I went with calls for 3 sticks of butter. With butter about $3 a pound, You're talking $2.25 just for the butter in that recipe. So being cheap, I decided to use 2 sticks of butter and 1/2 cup of Crisco instead - and surprise, surprise: The cookies came out better than ever. I've been using the same mix of fats since then.
So what is the deal with different fats in baking?
Butter (about $3 a pound or 2 cups) - Butter is pretty much considered the best tasting of the fats. It has a nice, rich, creamy taste to it. Butter comes from the fat from cow's milk - but it's about 80% true fat and the other 20% are milk solids and water. Typically, butter can give a crispier feel to things like cookies. When buying butter, you're faced with the choice of "salted" vs. "unsalted." You want unsalted. The reason some butters come in a salted variety is not for taste - it's used as a preservative. It keeps the butter fresher for a longer period of time. If you are baking, you do not want to use salted butter. It makes the dough tougher with the added salt. Butter is the most "natural" of all the fats. Little to no chemicals in the process of making butter (depending on the brand, of course).
Shortening ($4-$6 a can - best value is at BJ's) - Crisco (a.k.a. shortening) was invented in the early 20th century. It's just a mixture of hydrogenated oils - typically vegetable. Which means they take vegetable oil and blast hydrogen into it. Shortening has an extremely long shelf life and is very inexpensive compared to butter and margarine. Because shortening is just pure fat - it has little to no taste (vs. butter and margarine that does have some dairy-ness to it). Some shortenings do come with an artificial butter flavoring. Because shortening is pure fat - it leaves it's final product more softer and chewier than baked product made with butter - but it can also leave products with a more "greasy" feel depending on the recipe. Shortening is by far the most frugal fat out there for baking.
Margarine (typically anywhere from $1.29-$3 a pound depending on brand/type) - Margarine is almost like a combination of butter & shortening. It's a mix of hydrogenated oils mixed with skimmed milk. Margarine can come in all different varieties and made in many different ways. Some margarines even come with butter mixed in. Standard margarine is at least 80% fat (like butter) and can be used in cooking recipes in place of butter. It won't change the nutritional value, but it will make for a lighter, softer product. You have to be careful when picking your margarine for baking - so many margarines these days are reduced fat - which typically means they have more water in them and the chemical composition of the margarine will not support the recipe. You also do not want to bake with the spreadable margarine that comes in tubs. It is not processed and made the same way as traditional stick margarine. Margarine can be easily substituted in things like chocolate chip cookies, oatmeal cookies, etc. But I wouldn't use it for recipes that desire a real buttery taste - like sugar cookies or shortbread.
So now what? Well if you want to bake and be cheap - keep a container of Crisco in the house. You can substitute it for butter as you wish. Just use caution: Not all fats are created equal. If you want that slight crisp you are used to in traditional Toll House Chocolate Chip Cookies - you will not get that with Crisco. If you are a "clean eater" or care about chemically processed foods - you probably want to stick with butter. Now off to put on my apron and start the day.