89 Euros= £64.
That is rather a lot of money...even for Dr. Schaarwachter's expertise :(
Sadly it's probably a reflection of the relatively restricted readership for such material - weighed against the very high production costs of a musicological analysis which includes extensive musical examples.
I would imagine they are price-pointing these volumes with the institutional, university and library market in mind - rather than the small number of private individuals who would spring for such a purchase.
As these things go, £64 sounds quite reasonable for two volumes containing 1,201 pages; one has only to look, for example, a the prices of books in Ashgate's catalogue to find an average price per page considerably higher than this and it has been so for many some years; yes, the "relatively restrited readership" and "very high production costs of a musicological analysis which includes extensive musical examples" (not to mention photographs) are indeed an issue that tends quite often either to keep prices for such works on the comparatively high side, or, where that's not the case, to mean that income from other more "commercially viable" publications under the same imprimatur tends to help to subsidise them. And just look how long it (of necessity) took its author to put it all together!
I can certainly recommend this work wholeheartedly.