system
A chat on subreddit /r/NoStupidQuestions
human
I don't know...

I've never owned a horse but a quick google places them at around $2,000 to $5,000 a year.

Between insurance and gas alone, you're already pretty close or over the lower end of those numbers and after a couple oil changes or tire changes in winter climates it seems like it would easily be comparable.  Add on the price of even a used car and you'd be able to create a pretty good argument that a horse is just flat out cheaper.
gpt
Look up the price of hay, oats and any other feed you might feed the horse.  Your costs will balloon very quickly.