It can be pricey. My 30g reef I recently setup was a little under $1,000. Thats also including some corals and the lighting.
Saltwater tanks can be as expensive or as cheap as you want. Normally the expensive ones tend to run a little stablier, but if your willing to put forth the daily effort, there are many cost cuts you can make.
For example, without a sump (seperate tank used for filtration and various things), you dont' need to pay $30 or so to get your tank drilled per hole, plumbing, the sump tank itself, the baffles to put in it, the silicone, and a return pump. Without a sump, your tank will still run (expecially if it isn't a reef) very well if properly maintained.
I have not read any saltwater based books yet (I know, I should), and having not read them, can't recommend any. If you search for books on these forums, you can probably find some good references.
The main thing also, the more research, the less you end up spending and the better your tank.
Good Luck!!! It is a lot of fun and a very rewarding expirience!!!