Using Richo's formula, TK is 42% as effective as DM, so the price might be good but is it good value.
I'm a fan of Kingston, but I feel he needs a year of grade and some quality peptides. Shouldn't be hard to find at the moment.
Ha. I was being very approximate.
You need to factor in a lot of things. How old are the players? How well do they fit the system? How well do they fit the need of the squad, etc.? To my mind, Kinston/Mitchell isn't an either/or proposition. They would be valued very differently and should be. Of the current outside backs, Turner is the most expendable/requiring of a rather large pay cut. He's old and probably on par with Kingston for Super Rugby impact.
A good example, IMO, of a team deciding that the price had exceeded valuation was the Reds with Higgers. It might have been tough to keep him under the cap, but they could have done so if they really, really wanted to. After his Super Rugby form last year, it would have been tempting for many organizations. But the Reds decided they could get 90% of Higgers from Ed Quirk at a fraction of the cost. Plus, they will likely be in the best position to sign Quirk to his next contract too.
As a side note, valuing players appropriately would be an excellent area for advanced statistics to assist rugby teams. I would hope that the smarter teams are building priority models to do so.