Saltwater can be a bit tricky but isnt really hard as long as you are up to the challenge. first of all you need to understand that in the ocean water quality NEVER changes... so if your tank water gets even slightly dirty you are in for trouble. You need to be able to provide a relatively stable enviroment otherwise you will do like many people and be fine for several months then your tank will crash and you will have to start from scratch.
That being said you can set up a tank for virtually the same cost as a freshwater tank if you are prepared to do weekly maintenance. This means having a place to have premixed and aged saltwater on hand at all water change dates. Or you can set the tank up for about 100x's that of a fresh water tank and do it right with live rock. I think you could set up a 30 gallon tank for roughly $150-300(depending on local price usually $5-10 per/lbs) worth of rock or 1 lbs per gallon.
As you can tell I dont recommend doing a tank without live rock I think it is a mistake and would even go so far as to recommend not even trying if you dont... but it is possible to do with out so I wont. Other then that you can have 1" of fish per 5 gallons during the first 6 months then another 1" per 5 gallons after that if you use live rock. So that means you need to choose your fish pretty carefully.
All in all I think my salt tank is very rewarding and not that much more difficult then my freshwater tanks now that I am used to it. If you are serious about setting one up I would go buy 2-3 books that discribe how to set up your first tank and read them each twice before buying anything the more you read the better it will be.... There is so much info regarding setup that it would take quite a while to try and explain it all outright, so if you have some specific questions that would make it a little easier for me... I could probably write myself into carpel tunnel syndrome otherwise

It would be good to have another bloke around who is into salt water so if I can help anymore just let me know.
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Adam
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