Ill start by answering your questions. Then give some basic hints.
Are the tanks different than your average aquarium?
Nope. Same tanks as you use in freshwater.
A reef tank describes a tank that has been setup to simulate the apperance of a coral reef. Reef tanks include fish, corals and other invertribrates like shrimp, crabs etc. A reef tank often has a sandy bottom and has a fair amount of live rock aswell.
By this question im thinking maybe you ment to ask above what a 'reef ready' tank was. A reef ready tank is simply an aquarium that has built in overflows and drains as well as often times built in returns for the use of a sump or wet/dry. Freshwater folks can use a reef ready tank and benifit from its design as much as a salty person.
Are they hard to keep up?
I have seen photos of your ponds and I would go as far as so they are no harder to keep than that pond is or your 100+ gal
freshwater tank. Once you develop a good schedule you can probably get buy with 15-20min worth of work a day or maybe 2-3hours a week.
Now as you know with any new venture something that you should do is plenty of research. This post is obvously the first step in such research. There are three main types of saltwater setups. You have a Fish Only setup, a Fish Only with Live Rock and a Reef. As you progress thru the setups the costs of the setup increases.
I would be willing to venture if you had to buy everything new i would say a 55 gal
tank from beginning to setup would run you $1500+ for a reef tank $750 or so for a FOWLR
and $400-500 for a FO