What kinds of corals are you going to be propagating and with what lights?
A shallower and wider tank would be more efficient than a long skinny tank. If you don't mind going custom made a 36" x 36" with a single 400 watt or 250 watt halide would be perfect.
the quote I got for a 48 inch long by 18 deep and 12 high was $400. need some help finding one a bit cheaper. I paid less than that for my 72 gallon bow front DT
keep an eye on ur local bargain posts.
you will get a really good deal on there.
my bro. got an almost brand new 120g with 2 canisters, sand and a bunch of stuff for the tank for only $250. what a deal.