Essential Solitude: The Letters Of H.P. Lovecraft and August Derleth, 1926-1931 (2 vols.) is about to hit paperback, according to a Hippocampus FB notification.
$50 for both. Although Americans using Amazon.com can currently snag a nice pre-order, for $40.41 the pair with free shipping. The books are also listed on Amazon UK at £41 ($63), so those of us in the UK get a better deal ordering direct from Hippocampus. Pricey, but a lot more affordable than the $750 Amazon U.S. is asking for the hardbacks!