I haven't worked directly with the SeaFLIR III, but I have limited experience with military grade thermal imagers.
Firstly, I can confirm that new, this would have cost in the realm of $300-500k USD depending on options. Keep in mind the target market was military and government customers, so the price usually includes project services as well as the equipment costs.
Next, the bad news. Most of the systems of this level that have made their way into public hands have been salvaged, and to conform with ITAR and other regulations, the contractors responsible have a legal obligation to disable them. The electronics will be stripped, and often the remaining hardware considered vulnerable to reverse engineering will be physically sabotaged. Even if you're lucky enough to find a unit with no physical damage, to reverse engineer the electronics would take time and resources that likely exceed the cost of a new system.
You can salvage the actuators, optics, mechanical components, and some electronics (e.g. EO sensor and laser), but you're extremely unlikely to ever get the MWIR sensor functioning again without the original electronics. The residual value for an early model SeaFLIR III system would be well under $5k in my opinion.