Soldering with silver-lead depoles PZT. Bismuth solder does not and regardless repoling PZT is trivial- a couple hundred volts at most, and temperatures below the melting point of plastics.
The transducer is the only part of the system that should concievably be expensive, though. Doctors don't use special, medical-company made laptops- they use thinkpads or dell or whatever. The cart is unnecessary! It shouldn't be where the cost is coming from. The cart should add a few thousand dollars. The electronics have no business costing tens of thousands of dollars. The R&D, the software, and the transducers are the only plausible money sinks. If making a monitor is expensive, the companies should buy a cheap laptop and write an application to run on it.
I do really enjoy your posts but I am firmly in the camp that the price of ultrasound machines is an order of magnitude too high. I also think it needs to come down ASAP and that the future of cancer treatment really depends on regular ultrasound screenings and machine learning.
Edit: also, to back up my statements about the electronics: https://news.ycombinator.com/item?id=13245998