Step Turn, you are not necessarily wrong, but I was trying to avoid the old single vs. twin discussion and just look at performance per buck spent.
My point was simply:
SEP: Won't do it. Low cost.
MEP: Will do it. Low cost.
SET: Will do it. High cost.
MET: Will do it. High cost.
So if cost is a factor, a piston twin is your best option. Gives the maximum bang for the buck. If cost is somewhat of a factor, but you're in the turbine realm, then I would argue that the MET is the next best choice as it has climb performance on one engine AND will be cheaper to buy into than a SET. It's safer, bigger and cheaper, simply because the SET concept is rather new and there are no old SET airframes on the market. If cost is no factor at all, buy a newish SET or a Jet.
I am myself moving to a MET as we speak, because of many things we talked about: It's safer and has better performance on one engine. It's faster and burns a fuel that's less expensive, making the cost per nm the same as an Avgas twin. Fuel is more flexible and accessible. Less things can go wrong and engine management and hourly service is greatly reduced (they just don't break down very much compared to piston engines).