Hey Otoe,
I used to bury my stone in the ground and build fires over them, but they require your time and a lot of wood or charcoal to get results. Sometimes it wouldn't get hot enough, other times it got too hot and shattered the stone. It's a lot of trial and error.
Seven years ago my dad bought me a small kiln and I absolutely love it. It works great and you can control the the temp precisely. As an added addition, we drilled a small hole in the top and inserted a thermometer into the interior of the kiln. You can see what the temperature is and control it to exactly the temp you want. My dad got the kiln from Steve Behrnes out of Louisiana. It is specifically designed for cooking stone, so it heats up very slowly. It's almost like those Ronco rotisserie cookers "Set it and forget it". If you plan on doing any knapping, I would suggest strongly that you get one. If you don't like it you can put it on the trading post on this website and easily sell it. Using a kiln will save time, effort, and stone.