This discussion would make a lot more sense if it were taking place 35-40 years ago, when you could go to a Beech, Cessna or Piper dealer and buy a new, corrosion-free airplane, with factory-installed options packages, and with something that passed in the aviation industry for a warranty. Those days are gone as to the types under discussion here, unless you want to pay a king's ransom for a new G36 Bonanza.
In the old days we could compare airplane types in a vacuum; now each individual example of each type must be scrutinized on its own merits. "All else being equal" is a meaningless phrase in this market of decades-old, complex machines. For example, there are 3,846 210s on the US civil register. No two are exactly alike. 3,846 different levels of use, damage, disrepair and neglect; 3,846 different panels full of jerry-rigged, aftermarket avionics and equipment.
Will a 210 cost less than a twin to operate? Serial number x might; serial number x+1 might not. All you can do is narrow down your search to the types (plural) that fit your mission, then find the very best example you can ... and hope for the best.