´Pyramid´ chair designed by Wim Rietveld for Ahrend de Cirkel - 6 for $3406 on 1st Dibs. One for around GBP200 on ebay now. Too pricey.
Or these, Eames DSW shell chairs, which are always splendid, and either cheap if we find them at the right place or overpriced from vintage dealers. The good thing is that the shells were used on a lot of different style bases so they are sort of ubiquitous but there are a lot of sources for cheap repro legs, like the dowel legs shown below. So, if we can find six shells in good shape, we can pick up the bases we want easily and put them together. Just an idea.