If you would like to experiment with cooking using energy free from the sun, a pizza box solar cooker is the cheapest and easiest entry-level step. The only things you will need to outright buy are tape and aluminum foil. If you have a good dollar store nearby then you've spent two dollars total - the rest of the items you can creatively scrounge for free.
A simple cooker like this can reach over 200 degrees F in direct sunshine. The key is pre-heating your cooker, then setting your food in for the day, covering the top with clear plastic, and leaving the food alone. By dinnertime your food should be cooked. You can even use a hay box to extend the warmth of your meal if you are not ready to eat yet. This type of of cooking doesn't use any electricity or fuel wood - hot meals can be yours for free on any day there is sunlight.
Frugal Ingredients for a Basic Pizza Box Solar Cooker
Cover the inside of the pizza box and lid with the foil. Tape the edges securely around the edges of all the flaps. I have two pizza boxes nested together to create two solar panels directing solar heat within.
Place your your box in direct sunshine and let preheat for about 20 minutes. The stick or piece of wood will help you angle the lid flap for the best solar angle. Add your food - for flat food, cover the opening with your clear plastic to retain heat. For wet food, place the liquids in your wide mouth jar and seal the lid. You can even paint the outside of your jar black to seal in the most heat.
It will take some experimenting to figure out cooking times, but you will find that the slow cooking enhances food flavors, and that it is difficult to overcook food this way.
Here is a link to a very cool idea book at Amazon: Cooking with Sunshine: The Complete Guide to Solar Cuisine with 150 Easy Sun-Cooked Recipes.