Nice. As Bill mentioned, there were three versions of this one. Aaron Krumhansl compiled the following information:
K57a - 54 copies hand-lettered by Roger Marcus, bound in green silk-covered boards, housed in a marbled slipcase and signed by Buk.
K57b - 750 copies in wraps; a paper version of what you have there
K57c - This is what you have: "133 signed copies were published 14 January 1977: 100 copies numbered 1-100, 26 copies lettered A-Z, the remaining 7 copies were marked "Author's Copy," "Calligrapher's Copy," "Publisher's Copy," "Printer's Copy," "Binder's Copy," "File Copy," and a "Presentation Copy" marked with the recipient's name. The copies lettered A-Z and the seven out-of-series copies were issued in a blue paper covered slip-case."
Abebooks lists numbered and lettered copies of K57c at $450-$600. Jeff Maser has the numbered copy at $450 and he is a great seller. Common thought is that market value (i.e., about what you might expect to get on ebay) to be about 20-25% less than a reliable abe price. But the market is poor at this time. In any event, your book is probably "worth" about $300 +/-. I'm a shade more optomistic than Bill on price here.