A bit of a wild shot, but check public libraries.
There may be a copy somewhere (not just in your country) and, if getting towards the end of its "service" life, it may be possible to purchase it, at a very reasonable price. Many (most) libraries also "sell off" books monthly, very cheaply.
I've searched, ln the past, and had some success this way, both with UK and European libraries.
One example was an out of print book, which I eventually found at a Dutch seller for around £60 (original publisher price £15), then found at a library somewhere else in the UK ( about 150 miles from my location) for £1 !!
Even with shipping costs it totalled around £6, and, although not pristine, it was in very good condition (hard back, minimum wear or fading etc), and had a clear "polythene" protective jacket cover as a bonus.
Worth a try.