I have found FX5's to be great canister filters. They move a lot of water and have a good amount of room for bio media. I used Seachem's Pond Matrix for my bio media. It is a porous rock of some sort and is just a larger version of the Matrix bio media. Any bio media will work, but it takes a lot to fill up the FX5. I personally run 2 FX5's on my 180 that had a relatively high bio load. Yes, they are expensive, but they are worth it in my opinion.
My advice to you is to make sure you save up enough money to set the tank up right. I set my 180 up a few years ago and was in a similar position as you where I didn't want to/have a lot of money to spend on setting up the tank. I ended up skimping on my filtration to start with, opting for an undersized Eheim canister and undergravel filtration of all things. I ended up upgrading all of the filtration within the first year and essentially wasted a good deal of the money I spent on the initial outlay. The most cost effective way to set up your tank would be either to get a drilled tank and use a sump or a dump filter on a non-drilled tank. There was another thread on the forum recently that described a dump filter, so check that out for details.
Good luck with it, but please make sure you are ready when you get your fish. Last thing you want to do is purchase hundreds of dollars worth of fish only to have them die because you don't have the right set up.
