John Baymore provided a list a while back. You can see the full list here:

http://lsv.ceramics.org/scripts/wa.exe?A2=ind0307B&;L=CLAYART&P=R12974

John stays at the first one. Said it costs \7500 a night and included breakfast and dinner. He also advises that you have a Japanese speaker call for you.

Okadaya Ryokan　0285-72-2016
Hasegawa ryokan 0285-72-2210
Shiraume-so 0285-72-6762
Tozan-so 0285-72-2063
Ohkawado Kozen Spa 0285-72-4546
Minshuku (private guest house) Higeta 0285-72-2559
Minshuju Furusato 0285-72-3156
Minshuku Yamaji 0285-72-2525
Minshuku Yamabiko 0285-72-1829
Business Hotel Toyoda 0285-68-4500

Furuki-san runs The Tao Art Club, Potters In, a traditional Minshuku style inn and also a pottery studio. Lodging only is \3500 a night. Cost more to use the studios. If you book during the week or "off peak" you might be able to stay in the Minka farmhouse, which has "Western" style toilets. If the Minka is full, you get placed in modern rooms, but with "traditional" modern toilets. It is located in a convenient spot. Fax first, Furuki-san can read English and then voice call to confirm:

FAX 　0285-72-4178 Voice: 0285-72-3866

Best way to get to Mashiko from Tokyo is by train to Utsunomiya and then bus from Utsunomiya to Mashiko.

Buy a rail pass before you leave home. You cannot purchase them once you are in Japan. They will save you a lot of money.

Check out http://www.japantravelinfo.com/ for travel information