Please try to compare again now.
Basically, non-inverter model has higher (50-130W) peak power consumption than other models.
That means even we run both in peak mode, users can enjoy better cooling experience and lower electricity bill.

The initial discussion was about saving electricity bill cost.
The purchasing cost was not considered.
If this has to be considered, please also factor in the gained features (fast cooling, ionizer, connectivity, etc) and experience (cooling effect).
Your formula can become (btu/watt + features + experience)/RM ratio.

The only cost concern is the part replacement for inverter models is significantly higher.
More features also mean more things can fail.
But this reliability can be subjected to brand, maintenance, installation, usage and etc.