Yogurt is easy to make. You don't need anything special to make it, so forget the excuse to buy a yogurt maker, even at a garage sale. You simply don't need it.
What you need is a good yogurt starter, which is simply a little bit of natural, real yogurt that doesn't contain anything but yogurt. Check the label; rule out the ones that use guar gum, sugar of any kind, fruit or flavorings. You want a yogurt that has live cultures in it because you can't make your own without them.
When you've found the yogurt (organic is best), take a cup or so of real milk from the refrigerator and put it in a well-scrubbed glass jar or bowl. Add a quarter cup of yogurt, stir it and put a lid on it loosely. Don't tighten it down; the lid is only to keep it clean. A cloth napkin or teatowel works just as well as a lid.
Now, set it in a warm place, like on the refrigerator or the top of the water heater or in an oven with a pilot light. Don't put it where it will get too warm - you want it pleasantly warm, but not hot or the live cultures will die. The best temperature I found was found on the top of an electric dehydrator (if you're frugal, you won't do this unless you're using the dehydrator for something else already).
Leave it at least 24 hours, then stir. If it's not done (taste it to see - it won't hurt you), leave it another 12 hours, then check again. How long it takes depends on how warm the environment is.
When it tastes like plain yogurt (slightly sour), it's done. Take a small portion to use as starter the next time, then you can flavor your yogurt or use it plain in place of sour cream in many recipes and on baked potatoes, etc.