It always ticks me off when people say that saltwater tanks are "SO EXPENSIVE!!" I think that the people that say this are people that are not thinking of the possibilities. If you don't want to spend a ton of money on a saltwater tank, then go fish only, or just stick to a smaller tank with a minimal amount of inhabitants. You can definitely do a saltwater tank with a very small amount of money, it is slightly more expensive if you directly compare a freshwater fish only to a saltwater fish only, but that is because of the synthetic salt you need to use in the saltwater tank. A properly maintained saltwater tank can be nearly the same price to keep compared to freshwater.
When you go with a reef tank then the sky is the limit on price, but if you get plugged into a local reef club you can get tons of different corals, inverts, and fish for prices that can't be touched by your lfs.
I definitely voted for saltwater, the diversity of life is much more interesting to view and maintain compared to a freshwater tank that just has some mildly colorful fish, plants, and maybe a couple of inverts.