It really depends on where you live. My experience has been buying everything second-hand and having impressive results.
My 120 gallon tank: $130
Stand custom built: $50
Used G1 Skimmer w sedra 2500 pump: $120
Live sand: 200 LB for $60 at a gardening store
Live rock: bought over a long period of time. got most of it for $1/pound.
two koralia 4s: $80
150W HQI DE metal halide setup: $100
175W SE metal halide setup: $100
then all the misc stuff that maybe adds up to $100-200
total estimate: $900-1000
It all depends on how new you want your equipment to be. For many people keeping a saltwater tank is a status thing. Sure it's nice to show off your hard work to people, but I get most of the gratification out of spending intimate time with the tank scrubbing and doing maintenance. That's when you know you're in it for the long haul.
One thing I have learned is that it is better to buy the tank new. I found some major dings that I didn't notice when I bought it. So you might want to buy that new or at least inspect a uesd one for awhile at every angle. Not to mention you'll know 100% that copper wasn't used in it.