Andrew I/we will try to help you out but I can tell you that all of my information is going to be based on USA prices I see your location is Australia so I have no idea what the equivlent would be in your area and im not sure how the Aussie dollar compairs to the American dollar as far as currency conversion so some things might be alot cheaper or more expensive based upon local economics.
Clowns are heardy overall and here locally you can get a pair of tank rased clowns for $15/each. Sea Horses on the other hand are not overly heardy and have some very specialized diet and enviormental needs that need to be meet.
Tank prices can differ widly thruout the US so I would have no idea as to what it would cost for you there. If you dont plan on keeping any corals then you can get by with a standard florecent light strip for lighting since the fish have no real lighting requirments other than something to simulate a day/night period.
Equipment you will need would include the following:
Hydromoter (to test salinity)
Test kits (ammonia, nitrite, nitrate, ph
at a minimum)
Salt mix (50 gal
bag to start out with but this will be something you will have to purchase on a regular basis)
Substrate (sand or crushed coral)
Live rock (if you intend to use live rock for filtration and decoration)
Heater (may not be needed in your area depending on your climent)
Water circulation pumps aka powerheads (needed to move water around)
Quatliy water source
Everything aside from the live rock above could probably be purchased for $200-250 range. The live rock depending on the amount could another $100.
If you use a DSB
and live rock you wont need an external water filter other than the skimmer. If you go with maybe a shallow sand bed and no live rock then you need to add to the list of equipment a good external canister filter.