Several years ago I discovered a very simple way to make yogurt. I use fresh milk from our goats, but way back in the early days of motherhood I used to make it with cow's milk from the grocery store. You'll also need a small container of plain yogurt with "live, active cultures".
Use 2 quarts of milk, 2 tsp of yogurt, and 1 cup of powdered milk. The powdered milk is optional according to my cookbook (Goats Produce Too! by Mary Jane Toth -- you can find it here) but I've never made it without. It makes the yogurt thicker. If you have less milk available, you can cut the recipe in half.
Warm the milk to 115*. Remove it from the heat and stir in the powdered milk, then the yogurt. Mix well and pour into clean canning jars (pints or quarts) and add lids.
This is where my method gets real easy. You don't need a yogurt maker or a dehydrator. I put the jars into a small insulated cooler, then fill the cooler up to the "necks" of the jars with hot water. Close the cooler and leave undisturbed for 6-8 hours. It's that simple.
I once had a batch that wasn't thick enough after 8 hours. I bailed out most of the water and refilled with hot water, and left it to sit longer -- overnight actually, as it was bedtime when I checked it. In the morning it was ready.
Don't forget to save some of this batch to use as a starter for your next batch.