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

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* 1. how many of the official sourcebooks do you posses?

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* 2. how much would you, at most, be willing to pay for a hardcover sourcebook?

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* 3. how much would you, at most, be willing to pay for a PDF sourcebook?

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