I like that site, he is a very knowledgeable dealer about early english furniture forms, really great pics plus he's very mindful about connecting Thomas Dennis ( americas most celebrated 17th century joiner) to any piece that is attributed to the shop where Dennis served his apprenticeship, to bring in the odd yank who might be interested. All in all, first rate web site.
Another point to keep in mind is, chairs are almost always going to be expensive because they are very rare in this era, only kings, queens and wealthy head of households sat on chairs, everyone else sat on stools. Indeed, in America, there are only 20-30 17th century wainscot (frame & panel) chairs known to exist.