I think these are the questions you should be thinking about when arguing against IP protection laws.
Edit: One thing you failed to mention is that the technology available after the patents expired was orders of magnitude more advanced than what was available in the 1980s. For this reason, it's simply a no-brainer that the cost went from $30k down to $1k.
Then there's the whole "maker" movement that happened to coincide with the development of 3D printers which meant that 3D printers had a decently sized potential market. Go back 5-10 years and people didn't even know what the hell a 3D printer was! So it's only natural that the original inventors didn't invest more in optimizing the design and making it cheaper.