price dnd sourcebooks

how much are you willing to pay for an official sourcebook?

hello, I’m doing a small project for my school, and i have decided to do it about the sourcebooks on dndbeyond. apologies for any spelling mistakes, English is not my first language.
i consider the following titles sourcebooks:
AcInc
DMG
EGtW
ERLW
EEPC
FToD
GGtR
ID:RotF
LR
MM
MMoM
MOoT
MToF
OGA
PHB
SCAG
SCoC
TCoE
VGtM
WBtW
WGtE
XGtE
1.how many of the official sourcebooks do you posses?
2.how much would you, at most, be willing to pay for a hardcover sourcebook?
3.how much would you, at most, be willing to pay for a PDF sourcebook?