I snagged a couple at auction in the last year or so, both in 80-85% condition. One has a couple of small rust patches and needed a rear sight and cost me £114 all in. The other was at the higher end of 85%, and no bits missing, but around the same price, maybe a bit higher (can't find the invoice). Both times felt I had got lucky.
In general, I would say that presentable standard 55s go for £150-175, in private sales, depending on demand. Mint, or Nussbaum (walnut), 200-plus. From a dealer, add a third to a half to those prices.