Yeah I hear you bud, The GPU situation is the same over here in the U.K. The price of all components are inflated at the moment. Stupid Scalpers and miners. Dam You All...lol
I guess I will try to muddle through this, it's supposedly the solution but I don't understand the steps.
go to [System/Library/Extensions ]copy
AMD7000Controller.kext
AMDRadeonX4000.kext
AMDRadeonX4000HWServices.kext
2:Edit AMD7000Controller.kext /contents/info.plist
IOPCIMatch
0x68101002(or 0x67981002 ) >>>0x66111002(your display id)
3:Edit AMDRadeonX4000.kext /contents/info.plist
AMDPitcairnGraphicsAccelerator
0x68101002(or 0x67981002 ) >>>0x66111002
4:Edit AMDRadeonX4000HWServices.kext/contents/info.plist
IOPCIMatch
0x68101002(or 0x67981002 ) >>>0x66111002
5:put in /Library/Extensions
AMD7000Controller.kext
AMDRadeonX4000.kext
AMDRadeonX4000HWServices.kext
6:config.plis
FixDisplay true
AddDTGP true
FakeID 0x68101002(or 0x67981002 )
Graphics
false all
iMac18.1
7:sudo kextcache -i /
8:reboot