The PV544 was produced along side the Amazon for a few years. They share some bits.
Spares-wise I estimate their availability to be equally as good as the Amazon.
Early PV444 cars have harder to find bits of trim.
There are quite a few of us here with PV544s / PV444s on this forum. I'm one of them. My car =>
https://www.volvoforums.org.uk/showthread.php?t=277319
Note these vehicles were never officially brought to the UK by Volvo so were only factory made as LHD examples.
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Here in Holland the price for a road legal PV544 will start at about 8K (euros) - early PV444s are often more expensive. Nice PV544s (with or with out modifications) go for about 15K to 20K here.
The "one" that people seem to value the most is the PV544 Sport version but as it is easy to change badges and a few engine bits fake versions are easy to stumble across...