Good species for beginners are Ficus, Schefflera, Aralia, Barbados Cherry, Lavendar Star Flower, etc. You might wantt o look on Amazon as they have links to other "stores", like Bonsai Boy of NY and others. This way you can compare. That is, if you're looking for something already in a pot that looks like something. Otherwise, you might want to, on a budget, start looking at "starter" trees. These are (usually) 1 or a few years old, with very little refinement. However, one in a 4-6" nursery pot will be quite easy, usually, to produce a reasonably refined mame or shohin bonsai out of. You also might want to check out e-bay for supplies and start plants. My personal preference for starter plant material is www.meehansminiatures.com as they are reasonably close, priced well, and have an excellent variety of species to choose from.
FWIW, I'd stay away from the Pomagranate unless you have a cold room. Most reports are that they do not last more than two years without the dormancy.