I would definitely recommend a protein skimmer for almost any size tank. I know that you're on a budget, but you can probably find a CPR Bak Pak for less than $150 and probably much less used. If you can find a Bak Pak make sure to pull that blue bio-bale junk out of it, there is no need for it. The skimmer should be the only physical form of filtration on your tank, no sponges or carbon. Run at least a 3" depth of live sand. Actually the sand doesn't have to be live, you can just use clean dry Oolitic sand and purchase high quality live rock. The rock should populate the sand bed. Even better would be to use uncured rock and let it cure in your tank, more likely to get better bio-diversity from the rock that way. Of course, if you go the uncured route, don't add the clowns or any fish until the cycle is complete! Be sure to have a good quality powerhead for circulation too because the entire contents of your tank (rock and sand wise) is now your bio-filter.