It should be noted that there's a nonobvious opportunity cost here; specifically, money spent on the more expensive product can't be invested.

For example, mechanical keyboards seem like something that costs more up front that's cheaper in the long run. They cost about an order of magnitude more than membrane keyboards, but last about ten times longer, so you only need one mechanical keyboard to ten membrane keyboards, so the cost equals out in the end. Since the typing experience is much better on mechanical keyboards, by paying more up front, you essentially get a much-improved typing experience for free.

But, the extra money you spent on the nice keyboard could've been invested (or used to pay down debt) instead. If there's a an annual real interest rate of 10%, then buying 10 membrane keyboards at $10 over 10 years and investing the money you didn't spend nets $45, not counting re-investing (1). Note that these numbers are made up to make the math simple; in particular, the real real interest rate isn't that high.

Also, the membrane keyboard you buy in year 10 isn't going to be the membrane keyboard you buy in year 1.

(1) Using present value, in year 1, instead of paying $100 (cost of the mechanical keyboard, ten times the cost of the membrane keyboard), I pay $10 and invest $90 which, at 10%, yields $9. In year 2, you pull $10 out of the investment to buy the second membrane keyboard, so now you have $80 invested, yielding $8 returns. 9+8+...+1 = (9^2 + 9)/2 = 45.