Always pondered
Is there a way to only run your ads on Bing ... and not Yahoo and Bing ?
Nope, pretty sure there isn't. Never been able to find it in the settings anywhere. Wherever Bing goes, Yahoo goes or the other way around.
All these two have is each other in their struggle with the big G. Would be interesting to be able to segment performance by Bing / Yahoo though
If you bid on the low side, you only get yahoo traffic though 
Depends on the geo I guess, all bing traffic is dirt cheap compared to Adwords traffic
100 % true.
Quality is not always there though.
It depends on country. In Australia and New Zealand, for example, you can do Bing only. In US on desktop they have traditionally been a single product.
With the new search deal and Yahoo's emphasis on its own Gemini, there will tend to be divergence once again between Bing and Yahoo, certainly on mobile and increasingly on desktop.