Check out the Wash DC Craigslist, too. Don't know how much you want to spend, but there are a few 55g tanks around $100, although hopefully you can do better than that within CCA.
+1 on the 75 John. 55g just is too narrow and has too little bottom space for territory. With the fish you are keeping and thinking on getting you will need all the territory you can get for your males to claim.