I'm planning to take a shortest course of ascetic practices Sanrou called( two days and one night ￥8000) in autumn. If you want to stay longer and experience harder ascetic practices,then you should participate in Sanzen(four days and three nights course ￥12000) Foreigners can also experience Zen meditation at Eiheiji temple. This area is covered with snow deeply in winter,so autumn is the best season for beginners.
If you are interested in ascetic practice at Eiheiji please contact the temple directly.
You can get more information about Eiheiji in English from the following URL.