Not to take away from your main point, but the capitalized total cost of ownership for a pony is _much_ larger than $1000 (which, by the way, is the price for a not-very-good-natured pony; breeds with nice temperaments cost a lot more according to https://pets.costhelper.com/pony.html ).
Doing some quick checking, food for a pony is ~$1-2k per year. Lodging is $2-3k per year. Basic preventative veterinary care is $1k per year; if the pony gets old this could get a lot more.
That's $4-6k a year for upkeep, and ponies live for 20+ years. So the actual cost of a pony, even with discounting and whatnot for future dollars, is probably at least $50k, not $1k.
If you really think through the implications of every individual in America owning a pony, it gets a lot more interesting than that! It means that everyone in every city would own a pony -- would that mean that perhaps a proxy ownership situation would occur, where you had a certificate of pony ownership, but the pony would be housed and maintained anywhere in the country that could do so cheapest? It would cost a lot more than 2-3k/year to house a pony in NYC! Let alone the sudden demand for housing about 5 million of them...
My guess is that these ponies would be kept in horrible conditions similar to the way domesticated cattle are raised for milk and meat. I would hazard that all of our assumptions about the actual price of ponies and maintenance would come down if we all needed to have a pony, and would come down by a LOT.
Doing some quick checking, food for a pony is ~$1-2k per year. Lodging is $2-3k per year. Basic preventative veterinary care is $1k per year; if the pony gets old this could get a lot more.
That's $4-6k a year for upkeep, and ponies live for 20+ years. So the actual cost of a pony, even with discounting and whatnot for future dollars, is probably at least $50k, not $1k.