It totally depends on your stove & the type of fuel it uses. Electric will require a nice thick bottom to cook food properly.
- A better set will distribute the heat more evenly & you'll create more edible food instead of turning the ingredient into carbon. Less likely to warp if you need to dunk it in cold/ice water to stop the cooking process.
- Cheap light cookware limits the types of cooking techniques you can use. Also will melt nicely in a oven that's heated over 400 degrees.
- You don't have to spend a lot of money. $20-$40 will get you a decent pan, but choose something that enables you to utilize your style of cooking & will accommodate the amount of food you need to prepare.
Most people don't really NEED a full set of cookware.