One of my favorite, inexpensive coyote calls is the classic rabbit distress mouth call. This call is essential to any coyote hunters arsenal and one shouldn't leave home without it. The great thing about this call is that it is small, lightweight, and very effective.
What this call does is make the sound of a rabbit that is in serious pain. You can control the intensity by how hard you blow. You can give a waaaa like sound by how you move your hand over the end of the call when you blow. There is a call out by Knight and Hale that can be reversed as a coyote howler. You simply take the mouthpiece from the endpiece and voila. I'm not sure how well it works, but it sounds impressive to me and I will be purchasing this toy very soon. The downside to these coyote calls is that if you don't use it properly, you won't get results. Therefore, you must know how to use the caller and the correct sequence to call.
When using a rabbit distress call, you are trying to imitate a rabbit being attacked. So you start out with a loud, high pitched cry, and slowly work the intensity down. Your initial calling sequence should be about a minute long. After the first minute, pause for no more than about two minutes. The next sequence of calling should be about a minute long and similar sounding to the first, except with a little less intensity. By this time the rabbit is getting tired and possibly closer to death, so it doesn't have the strength to cry as it did before. After this, hold off on calling for about 5 minutes, then resume with the same sequence over again. Remember that you are directing the attention of the coyotes directly toward you, so your movement has to be kept to a minimum.
Remember that location is always important. I have said this before and I will say it again. Set yourself in a spot where your eyes can cover a large area. You want to see the coyote coming. If you are in a field and not sure where to sit, go to the side closest to any human involvement, like a road or house. It is my experience that coyotes always come from locations farthest from where people are. Well that is enough for now. Remember, if you ever have any questions, just ask :).