If you are short on cash you can buy a .5 gallon hex tank (plastic or glass it doesn't matter). Cover the outside of the tank with construction paper or brown paper (that's mainly only if the incubator happens to be in your bedroom and you don't want the light to keep you awake). Then put in about 2 inches of vermiculite or sterile soil. Keep it turned on for a few hours and then check the temp with a reliable digital thermometer. If it's too cold add more substrate or use something else to raise the eggs closer to the light. If it's too hot buy a $16 rheostat and use that to turn it down until it's just right. The only problem with this setup is that if your room's temperature extremely fluctuates then it will affect the temp of the incubator. A few degrees won't cause any major harm but it if is way too hot for too long then the eggs will dry out. You'll also want to spray the tank from time to time.
For $100-250 you can put together a much more reliable setup. The expensive part is the temperature controller . This setup also requires less maintainance. If you have that kind of cash here is where the details are;
The great and wise Family Zoo's incubator