I'm not sure there is any such thing as a cheap coral; they are all pretty price. As SH says the best thing is to go away and read about corals in general. Specific genera to look at would be Zoanthus, Palythoa, Xenia and Mushrooms (not sure on the taxonomy for these); you need to look at the specific needs of the coral which is related to the natural environment in which the coral is found. Feeding, lighting and water flow are all important. In here there are threads relating to the needs of corals, fish and other invertbrates; look on the home page for this group of forums it is the second one down from the top on the page. Select the topic you want and read the various entry.
Hope this helps
Regards