i'm going to disagree with newt. skimmer, coral sand, (bought) LR, lighting and powerheads, aren't necissary. i had a 10 gallon BSJ tank that just had a heater, filter and standard floro lights.
a fish only tank can actually be very inexpensive (by aquaria standards) a FW set up, with a calcium based sand, dry lace/holy/limestone/tufs/lava rock and saltwater is the ony things you NEED (well and a hydrometer and salt).
a skimmer help alot in bigger tanks (under 30 gallons and WC's should be enough)
unless you want to start getting into corals/other inverts/delicate/hard-to-feed fish.
i see no NEED for an expensive set up.
now WANTING one is a completely different story.