Here is where to begin: What clone do you want to be? A standard grunt white clone, an Episode II or Episode III clone, a clone commander, and animated clone, etc (and I know I didn't hit all the variations). Once you decide that, you will have some idea of what you will need to buy. On CT.net, you can use the search button there or check the for sale section to get an idea of vendors, etc.
Also, some thought needs to be given to how you will look in armor. If you are a skinny dude, you can pull off most any clone. If would be considered a little 'healthy', you might want to stay away from an animated clone version. If you are 6'4", I would recommend building a Vader, lol.
As Skip has already pointed out, this is not going to happen overnight. Any clone takes a while to build if done correctly. And, so you don't have sticker shock, depending on the clone you build you could easily spend between $1,000 to $1,500 or more (and that doesn't include the tools you might need to buy). That is why we are saying to take your time and do your research.
I 100% agree with Skip telling you to come out to an event and see some armor up close. That will give you an idea of what is involved. I would be happy to help you out as well.
Hope that helps.