interesting, but as someone who grew up on a farm (and saw the some of our "pets" put down so we could eat them) I think you end up with a different perspective...but then perhaps it was an economical one was well. back then we were a big family that needed the 5 pound blocks of government cheese to get by, so no doubt $10 would have been more than my parents would have spent to keep a pet.
there were a few animals that i can remeber being glad to see them go...the bull that used to chase us around the 40 acre field that my dad had to shoot 5-6 times point blank with escalating calibers of guns (with a few rounds in his head he managed to knock my dad on his ass right in front of us). my dad went back into the house to get the .44.
then there was the sow we had that ate all her young and would chase us around the moment we got in the pen. she was much more frightening than that bull. i was glad to see her go.
but most of our animals had names (i can't remember what we called the two above), even some that we were raising to eat. i realize that these are different than "companion animals", but it still makes me think differently about animals and how much we would spend. now that i'm cityfolk, i guess i would spend a bit on our cat, but at the same time she is getting old and i would weight that as well. no sense in prolonging the life of a critter that would be prolonging its suffering.