Walmart sells one pound tubes of Pride of the Farm taco-seasoned ground turkey for about $1.18.  I like to take two of these tubes, thaw them out completely, then cook the meat in a large pot until it's thoroughly cooked and any water boiled off.  Then mix in a can of vegetarian refried beans, which you can generally get for around 75 cents to $1.  The refried beans make the meat smoother and creamier.  Vegetarian refried beans are healthier than traditional (which is made with lard) and taste better than fat-free.

Heat hard taco shells in the oven to make them crisp, or warm corn or flour tortillas in the microwave for soft tacos.  Spoon the meat into the shells, then add your favorite toppings (lettuce, tomato, cheese, sour cream, taco sauce, etc)

This makes just shy of 3 pounds of meat, which is a hell of a lot of tacos.  Any leftover meat you can put in the fridge and reheat in the microwave for nachos later.  Or more tacos.