Hello !
After a lot of trial and errors .. Posting and reading posts , overheated / burnt ESC and a never ending hunt for a wattmeter decided to do some DIY stuff
Here it is
A DC ammeter a shunt resistor and a volt meter is what you require
Rest every thing is quite straight forward
You need to connect the ammeter in between the ESC and Battery and the voltmeter ( a digital one available at LHS for 300 bucks ) at the charging end.
Run the motor with the prop at full throttle .. Chect the current and voltage .... Record it
Then some maths ...
P= I*V where P is power and I is current and V is voltage
( one tachometer if available can really get you all that you need right now this is the setup ... Tachometer will be added soon )

Actually if you a use a shunt - you can use a multimeter as a wattmeter

better to buy a multimeter from your local market

Tess but calculating the shunt value  would be a issue and it won't give you a direct reading ...

Typo Tess = yes

A DC ammeter comes with a precisely calibrated shunt and will give you a direct reading .. And for a layman like me its better