Just completed as an auction, a complete set of Selected Letters of H.P. Lovecraft on eBay UK, with 19 bids from eight bidders. As such, the final price of £180 inc. postage usefully establishes something of a 2019 baseline price for a less-than-perfect but clean and readable set with dustjackets, in the UK and without any plumping of the price by a professional bookseller.
I was high bidder for a bit but wasn’t engaged enough to snipe.