The JDM 6 speed will definitely NOT be your cheapest option. You have to buy the entire gearbox, not just the gear set and they are pricey, even used. You'll need a miriad of other new parts as well. Some companies were originally charging around $9k for a full driveline conversion. Some people have managed to do the swap without all of the recommended hardware (half shafts, primary drive shaft, etc), but the gearbox itself will run you more than most of the hardened five speeds on the market. My latest research and discussions with people who've actually driven the 6 speed seem to indicate that, while it's a great tranny, it's not the holy grail. You'd be better off with a hardened five speed with closer ratios.

Billy's Kaaz set and the Chalak gears you mentioned earlier are both cheaper than the going rate for STi 6-speeds. Something to consider.