I am talking to those who may not know much about computers [and have the most efficient buy]

The first is to always understand what you need before you buy.

The next strategy for minimizing the cost of computer ownership is to develop the habit of using efficient software in order to put off buying new hardware for as long as possible. [...] Over the long term, renting almost anything is more expensive than buying.

Amazon sells used computers, but the best place to shop online that I have found is EBay. (EBay is not paying me to say this.)

and more in-depth tips