it may appear like they are cheaper but that is paying for the car in japan... on top of that once the seller has put it on the ship you have to remember to budget for cost of the Shipping, the Import Duty (10%),the VAT (17.5%),the Customs fee, the Shipping Agents fee, the SVA or MOT test preparation and the cost of the SVA or MOT itself.
as steve said, its probably best you just get one here coz on top of all that, my biggest worry would be buying from a genuine exporter.