Well, to be honest, if you're willing to do a lot of regular maintenance on it, it can be pretty easy to trasfer over. Though, the larger the tank, the more expensive the investment, cause you NEED lots of live rock for filtration...I have 2 little saltwater tanks, my display tank and my quarantine tank. They're 4 gallons each, and the display tank is hooked up to a home made 10 gallon sump...All my shit is ghetto rigged in place, cause the build is half the fun, for me.
I also have a 36 gallon bowfront tank...It holds my 2 little itty bitty goldfish whom I've named "Chips" and "Fish"...I eventually wanna convert that to a 36 gallon Saltwater tank so I CAN have some saltwater fish, but my current SW tanks are only large enough for a small Goby each, and I desire a more free-swimming fish.
But...if u DO decide to start a SW tank, I can shoot you some good beginner corals.