If there was a simple formula that worked to calculate power required to hover, all of us in the flight test business would be out of work!
An approximation can be found in "Helicopter Performance, Stability and Control" by Prouty, but you will still have to wade through the text.
I couldn't work out how to insert mathematical symbols in my reply to this forum. Send me an email and I'll gladly respond with the best approximate formula that I know of for power required to hover
[email protected]