if you don't want to heat your raw milk to around 180 to kill off the existing bacteria, you're going to end up with runny yogurt pretty much no matter how you do it. at least that's been my experience. you can, however, buy yogurt starter made for use at room temperature that comes with specific instructions for raw milk from culturesforhealth.com - run by a MDC mama, great customer service. that'd probably be a lot cheaper than a yogurt maker.
if you don't mind heating the milk, heat it to 180F before adding your starter, and let it sit for a long time. i do mine for like 12 hours. when i used pasteurized/homog. milk i only cultured it for like 6-8, but the raw milk needs the extra time to thicken up IME. then as long as you can maintain the temperature around 110F you should be fine. some people do that in the oven with the light bulb on, or in their crock pots, or if you have an excalibur dehydrator you can do it in there. until i got my dehydrator i just used a small igloo cooler, did 2 quarts at a time, and wrapped everything up in towels, and that was sufficient to maintain the temp.
also, if you do end up buying a yogurt maker, try to find one where you can use quart mason jars in it, or that comes with glass cups. the plastic ones have BPA.
HTH!