Any risk analyst could tell you all the factors you don't take into account when you do a simple comparison of renting a new, cared-for, insured vehicle for which someone else is responsible vs. the crapshoot of buying something second-hand, which you now have to take on, whatever goes wrong.
I also doubt you are taking fuel into account with this comparison, which was the primary source of savings mentioned when you own a small car and rent a truck as needed.
Come now. Most of the people who drive pickups rarely if ever use them to tow or haul things. They drive pickups because driving anything else means you're gay, or communist, or smoke marijuana.