Having imported things from Japan I think you will find that customs very easily find things thrown in boots. Not only will you have to pay duty and VAT but the company importing will be heavily fined for trying to sneak an item in. I doubt you'll find anyone to do it that way.
Unfortunately when you add shipping, agents fees, duty, VAT, customs and handling + transportation fees it all adds up. Double sounds a bit high but I generally found that you paid at least +50% on the original price. So buy for £500 expect to pay £750 minimum delivered, in reality more. The other problem is the pound is so weak now it has almost lost half its value against the yen in the last 3 years. This means the price if you are paying in pounds but having to convert to yen can fluctuate over night. Hence why I no longer bother to import as nothing can be had for cheap right now.
However, find a company that will do this for a fixed price and you may be able to keep some of the costs down.