I've never ordered anything from that site, so I'm not sure how reputable it is, but it does appear to be a bargain price. That price does not include shipping, which looks to be about $36 to my ZIP code.
You can purchase the HHKB Pro JP directly from PFU Fujitsu from their online store, for ¥24,990 (currently about $317). You have to use a proxy shipping service, such as tenso.com, and the EMS shipping plus service fees will run about $50.