Which type of clone are you looking to build ? Are you looking for 501st standarts, or pepakura type (cardboard+resin, bondo) would be enough ?
The best place to look for 501st is CTN, which is official detachment. However I have to warn you that posts like: "I want to be a clone, where can I buy" are not really wlecome there. It's best to do some reading first (I know, may be boring, but it's how it works) and then ask by PMs. Eg. someone has a WIP and you like his armor etc. so you ask where he got it.
And just to warn you- armor is not cheap and is really time consuming. Think that around 1k$ for budget will be enough, but if you look for quality, then it's def. more.
