I posted without actually reading ALL of your post Lomaca.
I read it, but didn't understand it.
I've read and reread now.
I still don't , but am close.

Concentrating on First selections only.
Supposing , just supposing, The Strike Rate is 30%.
The AVERAGE Dividend I need to get is $3.50 to make a Profit.
And just suppose I sorted My Database and found that the AVERAGE Price of My Top Selections was $4.50
These AVERAGE Prices you mention Lomaca , I figure you mean AVERAGE Prices of the Winning Selections.

So supposing I back tested and had wagered $1 on every one of My Top selections in a database of 1,000 Races.
I found that I had 300 Winners.
And I found that I would have had $1,350 returned for my Total Outlay of $1,000
My Strike rate is 33%
My AVERAGE Winning Price is $4.50

I can't work out My MINIMUM Acceptable Price.
Could you work it out for me Lomaca please, or do you need more information?