I am converting a 46 and here are some of the costs I have had so far.
$550.00 - Cannister Filter, 36" 2 Lamp T5 Fix (should have went better), Glass Top, 40 Lbs of Live Sand, one bag of salt, new heater.
$60.00+/- on 2 power heads for tank
$30.00 +/- on power head for mixing salt
$80.00 on RO
filter for water.
$150.00 for 20 lbs of live rock and 10 lbs of base rock
$30.00 on misc buckets and stuff from HD
$170.00 on live stock so far. Includes 2 clowns, 1 Six Line Wrasse, 1 Fire Shrimp, 3 Emerald Crab, 15 snails, 10 hermit crab, 2 small frags of coral.
It is a lot more work getting it set up but then it tapers off. It will always be more work though than the fresh water. You would think it wouldn't be worth it but I wouldn't go back to freshwater for nother. Mater of fact, I want a bigger tank. LOL