Is there anything of similar power ac off the shelf preferably with dual shaft?
I don't think you'll find any modern EV motor with a dual-ended shaft, because there is no reason to want two shaft outputs. In those rare cases where a motor is designed to be stacked end-to-end (transmitting each motor's output through the next motor's shaft), it will probably have a female spline in one end, rather than two protruding shafts. The
YASA 400 is an example of a motor which has a female spline right through it, so multiple motors can be stacked on one splined shaft.
Typically "pancake" style motors (relatively large diameter and axially short) are more likely to be designed to stack; YASA is an example.
The Tesla drive does seem to be quite expensive and the concept I had in mind hinged mainly on finding them salvaged.
Tesla Model S/X motors are the most common EV motors which are available in salvage and have a high power rating in the original vehicle. On the other hand, most EV manufacturers rate their motors for continuous duty, and some of those motors may be just as capable as Tesla's.
At some point the costs of extra mechanical complexity and multiple inverters will probably exceed the cost of just getting the right motor to start. That silly cigarette boat is designed to be visibly expensive - it's all about conspicuous consumption.
There are some really big motors made for large vehicles. Pushed to higher than rated power for brief periods (and a Tesla motor can only produce its rated power for a brief period), just one of them might be a better solution.
TM4 makes some big stuff for trucks and buses, but I don't know how to get them at retail.