It really depends on what you want to do. Reef tank,
FOWLR. I am not sure of the price of a 100
gal tank. I just spent $260 on a 72
gal BF from Oceanic. for a 100
gal with all of the extras you should plan on spending at least $1200- $1500. This does not include substrate o live rock. Lighting alone can cost you anywhere from $200 to $600. Depressing huh?
IMO, it is money well worth it.