Since it’s long out of print, your best bet is the secondary market:
: You can frequently find listings on eBay or Amazon (via third-party sellers), with prices typically ranging from $35 to $90 depending on wear. Volo's Guide to All Things Magical (AD&D Forgot...
: Sites like Noble Knight Games often stock used copies, currently priced around $75.00 for Very Good condition. Since it’s long out of print, your best