there's always this one!!
it's only 60.00 on amazon.com! lol
seriously though, your best bet is using the search function, reading the posted thread above, and checking every single day in the cargo hold with your fingers crossed and a nice sized bank account.
I've put about 1800.00 in mine now, and its pretty much done. But I know a LOT of people who have spend A LOT more than that to do theirs (using metal parts and BM armors and such). Some have done it for a lot less with different quality of parts (making the armor themselves out of trash cans)
I've picked a pretty good balance, using high quality for some parts, and making my own smaller parts to save $$ where I can. But its taken me about a year to finish it. So if you can imagine, its VERY rare for someone to sell their armor they spent so much effort working on. When it does happen, its usually for 2500+ dollars. And its usually kinda sad
Be very careful with eBay too, cause a lot of the stuff sold there is kinda lower quality than what you can find around here with some effort.