Why do prices for different variations of the same engine vary
significantly? For example, factoryengines.com lists about 200
different variations of the TSIO520 for many different airframes.

Many datapoints between the high and low costs can be found, and of
course, you generally pay more for the higher HP engines.

For example:
The TSIO520B15B (285hp for C310P/Q/R) weighs in at $27k rebuilt.
The TSIO520BE3B (310hp for Malibu) is $51.7k rebuilt.
The TSIO520WB3F (325hp for B58TC/P) is $49k rebuilt.
The TSIO520VB6F (325hp for C402) is $29.3k rebuilt.

So the question is why is the Malibu engine 80% more expensive than
the C310 engine?

Is the difference in pricing volume driven? Accessory costs?
Fundamental differences in the engine design? Are the TBOs different
(1200hrs vs 2000?) that might make a significant difference in what
I'd pay for an engine.

A comment: Given that the C402 engine is $20k cheaper than the B58
engine, it seems someone should develop an STC that allows installing
the C402 engine on the B58 airframe. I know STCs are expensive to
obtain, but the margins seem very high on this deal, so I would think
it is a business opp for the right person.

-Nathan