Could run you quite a bit. If you want to pinch your pennies, you could try building your own protien skimmer. (Do a web search for "Skimmer Design 101".) Parts will run you around $20-40, plus another $20-40 for a pump to run it. If you want corals on a budget, build your own light hood with a VHO ballast and either Power Compact or conventional florecent endcaps. (T-5, T-8 or T-12.) That could run you around $200 for a high quality ballast, but if you get something nice like the IceCap 430, you can "overdrive" conventional (read cheaper and available at the hardware store) bulbs instead of paying the higher prices for VHO specific bulbs.
If you want to stick with fish only, you can skip the skimmer and the fancy light hood, but in my opinion, if you're looking for a cool looking tank, you either need corals or some impressive/expensive specimen fish.
Hopefully your rock is good stuff, just dead. Live rock runs $4-$6 per pound. You only need a small piece to seed your tank with coraline algae. This will work with either the fancy setup or the fish only one.
Live sand: You can pay a few dollars per pound for live sand, or you can get a few pounds per dollar for "Tropical Play Sand" at northeastern US Home Depots. (They are not allowed to sell it for aquarium usage but it's the same stuff from the same mining operation as the stuff Carib-Sea sells for alot more money.) Once again, just a small ammount of live sand from another reef aquarium is all you need to get the live sand started. Your LFS may give/sell you a cup of sand from an established tank, or you may be able to find someone on the classified section here who will sell you some cheaply.
For a sump, you can use a $5 rubbermaid container, but the pump may run you $50 or more, as it will need to be powerful enough to push the water all the way back up to the aquarium at a decent rate. A premade hang-on overflow box may be pricey, but you can use the extra solvent, and narrow pipe from the skimmer, with some extra fittings to make do. See thread:
https://www.saltwaterfish.com/vb/show...light=overflow
So overall for a reef setup, $400 at minimum, then you have to start buying corals at $40+ apiece.