Yeah, bio-cudes are great but they can cost alot new. I see bio-cubes all the time on craigslist, though. You could try looking for a craigslist deal. I don't live in a big town, so I search craigslist on a huge town near me that always has tons of stuff.
When it comes to stocking, clownfish are excellent for a 30g. They will do fine with a variety of other fish. They don't do well with damselfish, however. If you have an idea of fish you like, you can ask on here and we can help you get a specific plan setup.
Synthetic sea salt mix has instructions on how much to put in the water. It can be somewhat pricey, so price the salt soon. As far as other chemicals, I am still figuring that out myself. The sea salt mix should be able to raise the pH abit (good thing). As far as chems there are de-chlorinaters (have to have this just like with FW), there are coral chemicals, fish medications, and liquid invertebrate food, etc. I don't know alot of coral chemicals because I don't have corals (other than skeletons) in my tank yet.
There are all kinds of filtration methods, I am not very skilled in that area so hopefully someone with more experience can help you with that. I think my tank might need a little bit more filtration, so that is something I will be looking into.
Hope this helps!